/*
    SDL - Simple DirectMedia Layer
    Copyright (C) 1997-2011 Sam Lantinga
    Copyright (C) 2010 itsnotabigtruck.

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

    Sam Lantinga
    slouken@libsdl.org
*/
#include "SDL_config.h"

#if SDL_VIDEO_RENDER_OGL_ES2 && !SDL_RENDER_DISABLED

#include "SDL_opengles2.h"
#include "../SDL_sysrender.h"
#include "SDL_shaders_gles2.h"

/*************************************************************************************************
 * Bootstrap data                                                                                *
 *************************************************************************************************/

static SDL_Renderer *GLES2_CreateRenderer(SDL_Window *window, Uint32 flags);

SDL_RenderDriver GLES2_RenderDriver = {
    GLES2_CreateRenderer,
    {
        "opengles2",
        (SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC),
        1,
        {SDL_PIXELFORMAT_ABGR8888},
        0,
        0
    }
};

/*************************************************************************************************
 * Context structures                                                                            *
 *************************************************************************************************/

typedef struct GLES2_TextureData
{
    GLenum texture;
    GLenum texture_type;
    GLenum pixel_format;
    GLenum pixel_type;
    void *pixel_data;
    size_t pitch;
} GLES2_TextureData;

typedef struct GLES2_ShaderCacheEntry
{
    GLuint id;
    GLES2_ShaderType type;
    const GLES2_ShaderInstance *instance;
    int references;
    struct GLES2_ShaderCacheEntry *prev;
    struct GLES2_ShaderCacheEntry *next;
} GLES2_ShaderCacheEntry;

typedef struct GLES2_ShaderCache
{
    int count;
    GLES2_ShaderCacheEntry *head;
} GLES2_ShaderCache;

typedef struct GLES2_ProgramCacheEntry
{
    GLuint id;
    SDL_BlendMode blend_mode;
    GLES2_ShaderCacheEntry *vertex_shader;
    GLES2_ShaderCacheEntry *fragment_shader;
    GLuint uniform_locations[16];
    struct GLES2_ProgramCacheEntry *prev;
    struct GLES2_ProgramCacheEntry *next;
} GLES2_ProgramCacheEntry;

typedef struct GLES2_ProgramCache
{
    int count;
    GLES2_ProgramCacheEntry *head;
    GLES2_ProgramCacheEntry *tail;
} GLES2_ProgramCache;

typedef enum
{
    GLES2_ATTRIBUTE_POSITION = 0,
    GLES2_ATTRIBUTE_TEXCOORD = 1
} GLES2_Attribute;

typedef enum
{
    GLES2_UNIFORM_PROJECTION,
    GLES2_UNIFORM_TEXTURE,
    GLES2_UNIFORM_MODULATION,
    GLES2_UNIFORM_COLOR,
    GLES2_UNIFORM_COLORTABLE
} GLES2_Uniform;

typedef enum
{
    GLES2_IMAGESOURCE_SOLID,
    GLES2_IMAGESOURCE_TEXTURE
} GLES2_ImageSource;

typedef struct GLES2_DriverContext
{
    SDL_GLContext *context;
    int shader_format_count;
    GLenum *shader_formats;
    GLES2_ShaderCache shader_cache;
    GLES2_ProgramCache program_cache;
    GLES2_ProgramCacheEntry *current_program;
	SDL_bool updateSize;
} GLES2_DriverContext;

#define GLES2_MAX_CACHED_PROGRAMS 8

/*************************************************************************************************
 * Renderer state APIs                                                                           *
 *************************************************************************************************/

static int GLES2_ActivateRenderer(SDL_Renderer *renderer);
static void GLES2_WindowEvent(SDL_Renderer * renderer,
                              const SDL_WindowEvent *event);
static void GLES2_SetClipRect(SDL_Renderer * renderer, const SDL_Rect * rect);
static void GLES2_DestroyRenderer(SDL_Renderer *renderer);

static SDL_GLContext SDL_CurrentContext = NULL;

static int
GLES2_ActivateRenderer(SDL_Renderer * renderer)
{
    GLES2_DriverContext *rdata = (GLES2_DriverContext *)renderer->driverdata;
    SDL_Window *window = renderer->window;

    if (SDL_CurrentContext != rdata->context) {
        /* Null out the current program to ensure we set it again */
        rdata->current_program = NULL;

        if (SDL_GL_MakeCurrent(window, rdata->context) < 0) {
            return -1;
        }
        SDL_CurrentContext = rdata->context;
    }
    if (rdata->updateSize) {
        int w, h;

        SDL_GetWindowSize(window, &w, &h);
        glViewport(0, 0, w, h);
        rdata->updateSize = SDL_FALSE;
    }
    return 0;
}

static void
GLES2_WindowEvent(SDL_Renderer * renderer, const SDL_WindowEvent *event)
{
    GLES2_DriverContext *rdata = (GLES2_DriverContext *)renderer->driverdata;

    if (event->event == SDL_WINDOWEVENT_RESIZED) {
        /* Rebind the context to the window area */
        SDL_CurrentContext = NULL;
        rdata->updateSize = SDL_TRUE;
    }
}

static void
GLES2_SetClipRect(SDL_Renderer * renderer, const SDL_Rect * rect)
{
    GLES2_ActivateRenderer(renderer);

    if (rect) {
        int w, h;

        SDL_GetWindowSize(renderer->window, &w, &h);
        glScissor(rect->x, (h-(rect->y+rect->h)), rect->w, rect->h);
        glEnable(GL_SCISSOR_TEST);
    } else {
        glDisable(GL_SCISSOR_TEST);
    }
}

static void
GLES2_DestroyRenderer(SDL_Renderer *renderer)
{
    GLES2_DriverContext *rdata = (GLES2_DriverContext *)renderer->driverdata;
    GLES2_ProgramCacheEntry *entry;
    GLES2_ProgramCacheEntry *next;

    /* Deallocate everything */
    if (rdata) {
        GLES2_ActivateRenderer(renderer);

        entry = rdata->program_cache.head;
        while (entry) {
            glDeleteShader(entry->vertex_shader->id);
            glDeleteShader(entry->fragment_shader->id);
            SDL_free(entry->vertex_shader);
            SDL_free(entry->fragment_shader);
            glDeleteProgram(entry->id);
            next = entry->next;
            SDL_free(entry);
            entry = next;
        }
        if (rdata->context) {
            SDL_GL_DeleteContext(rdata->context);
        }
        if (rdata->shader_formats) {
            SDL_free(rdata->shader_formats);
        }
        SDL_free(rdata);
    }
    SDL_free(renderer);
}

/*************************************************************************************************
 * Texture APIs                                                                                  *
 *************************************************************************************************/

static int GLES2_CreateTexture(SDL_Renderer *renderer, SDL_Texture *texture);
static void GLES2_DestroyTexture(SDL_Renderer *renderer, SDL_Texture *texture);
static int GLES2_LockTexture(SDL_Renderer *renderer, SDL_Texture *texture, const SDL_Rect *rect,
                             void **pixels, int *pitch);
static void GLES2_UnlockTexture(SDL_Renderer *renderer, SDL_Texture *texture);
static int GLES2_UpdateTexture(SDL_Renderer *renderer, SDL_Texture *texture, const SDL_Rect *rect,
                               const void *pixels, int pitch);

static int
GLES2_CreateTexture(SDL_Renderer *renderer, SDL_Texture *texture)
{
    GLES2_DriverContext *rdata = (GLES2_DriverContext *)renderer->driverdata;
    GLES2_TextureData *tdata;
    GLenum format;
    GLenum type;

    GLES2_ActivateRenderer(renderer);

    /* Determine the corresponding GLES texture format params */
    switch (texture->format)
    {
    case SDL_PIXELFORMAT_ABGR8888:
        format = GL_RGBA;
        type = GL_UNSIGNED_BYTE;
        break;
    default:
        SDL_SetError("Texture format not supported");
        return -1;
    }

    /* Allocate a texture struct */
    tdata = (GLES2_TextureData *)SDL_calloc(1, sizeof(GLES2_TextureData));
    if (!tdata)
    {
        SDL_OutOfMemory();
        return -1;
    }
    tdata->texture = 0;
    tdata->texture_type = GL_TEXTURE_2D;
    tdata->pixel_format = format;
    tdata->pixel_type = type;

    /* Allocate a blob for image data */
    if (texture->access == SDL_TEXTUREACCESS_STREAMING)
    {
        tdata->pitch = texture->w * SDL_BYTESPERPIXEL(texture->format);
        tdata->pixel_data = SDL_malloc(tdata->pitch * texture->h);
        if (!tdata->pixel_data)
        {
            SDL_OutOfMemory();
            SDL_free(tdata);
            return -1;
        }
    }

    /* Allocate the texture */
    glGetError();
    glGenTextures(1, &tdata->texture);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(tdata->texture_type, tdata->texture);
    glTexParameteri(tdata->texture_type, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(tdata->texture_type, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(tdata->texture_type, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(tdata->texture_type, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexImage2D(tdata->texture_type, 0, format, texture->w, texture->h, 0, format, type, NULL);
    if (glGetError() != GL_NO_ERROR)
    {
        SDL_SetError("Texture creation failed");
        glDeleteTextures(1, &tdata->texture);
        SDL_free(tdata);
        return -1;
    }
    texture->driverdata = tdata;
    return 0;
}

static void
GLES2_DestroyTexture(SDL_Renderer *renderer, SDL_Texture *texture)
{
    GLES2_TextureData *tdata = (GLES2_TextureData *)texture->driverdata;

    GLES2_ActivateRenderer(renderer);

    /* Destroy the texture */
    if (tdata)
    {
        glDeleteTextures(1, &tdata->texture);
        SDL_free(tdata->pixel_data);
        SDL_free(tdata);
        texture->driverdata = NULL;
    }
}

static int
GLES2_LockTexture(SDL_Renderer *renderer, SDL_Texture *texture, const SDL_Rect *rect,
                  void **pixels, int *pitch)
{
    GLES2_TextureData *tdata = (GLES2_TextureData *)texture->driverdata;

    /* Retrieve the buffer/pitch for the specified region */
    *pixels = (Uint8 *)tdata->pixel_data +
              (tdata->pitch * rect->y) +
              (rect->x * SDL_BYTESPERPIXEL(texture->format));
    *pitch = tdata->pitch;

    return 0;
}

static void
GLES2_UnlockTexture(SDL_Renderer *renderer, SDL_Texture *texture)
{
    GLES2_TextureData *tdata = (GLES2_TextureData *)texture->driverdata;
    SDL_Rect rect;

    /* We do whole texture updates, at least for now */
    rect.x = 0;
    rect.y = 0;
    rect.w = texture->w;
    rect.h = texture->h;
    GLES2_UpdateTexture(renderer, texture, &rect, tdata->pixel_data, tdata->pitch);
}

static int
GLES2_UpdateTexture(SDL_Renderer *renderer, SDL_Texture *texture, const SDL_Rect *rect,
                    const void *pixels, int pitch)
{
    GLES2_TextureData *tdata = (GLES2_TextureData *)texture->driverdata;
    Uint8 *blob = NULL;
    Uint8 *src;
    int srcPitch;
    int y;

    GLES2_ActivateRenderer(renderer);

    /* Bail out if we're supposed to update an empty rectangle */
    if (rect->w <= 0 || rect->h <= 0)
        return 0;

    /* Reformat the texture data into a tightly packed array */
    srcPitch = rect->w * SDL_BYTESPERPIXEL(texture->format);
    src = (Uint8 *)pixels;
    if (pitch != srcPitch)
    {
        blob = (Uint8 *)SDL_malloc(srcPitch * rect->h);
        if (!blob)
        {
            SDL_OutOfMemory();
            return -1;
        }
        src = blob;
        for (y = 0; y < rect->h; ++y)
        {
            SDL_memcpy(src, pixels, srcPitch);
            src += srcPitch;
            pixels = (Uint8 *)pixels + pitch;
        }
        src = blob;
    }

    /* Create a texture subimage with the supplied data */
    glGetError();
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(tdata->texture_type, tdata->texture);
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glTexSubImage2D(tdata->texture_type,
                    0,
                    rect->x,
                    rect->y,
                    rect->w,
                    rect->h,
                    tdata->pixel_format,
                    tdata->pixel_type,
                    src);
    if (blob) {
        SDL_free(blob);
    }

    if (glGetError() != GL_NO_ERROR)
    {
        SDL_SetError("Failed to update texture");
        return -1;
    }
    return 0;
}

/*************************************************************************************************
 * Shader management functions                                                                   *
 *************************************************************************************************/

static GLES2_ShaderCacheEntry *GLES2_CacheShader(SDL_Renderer *renderer, GLES2_ShaderType type,
                                                 SDL_BlendMode blendMode);
static void GLES2_EvictShader(SDL_Renderer *renderer, GLES2_ShaderCacheEntry *entry);
static GLES2_ProgramCacheEntry *GLES2_CacheProgram(SDL_Renderer *renderer,
                                                   GLES2_ShaderCacheEntry *vertex,
                                                   GLES2_ShaderCacheEntry *fragment,
                                                   SDL_BlendMode blendMode);
static int GLES2_SelectProgram(SDL_Renderer *renderer, GLES2_ImageSource source,
                               SDL_BlendMode blendMode);
static int GLES2_SetOrthographicProjection(SDL_Renderer *renderer);

static GLES2_ProgramCacheEntry *
GLES2_CacheProgram(SDL_Renderer *renderer, GLES2_ShaderCacheEntry *vertex,
                   GLES2_ShaderCacheEntry *fragment, SDL_BlendMode blendMode)
{
    GLES2_DriverContext *rdata = (GLES2_DriverContext *)renderer->driverdata;
    GLES2_ProgramCacheEntry *entry;
    GLES2_ShaderCacheEntry *shaderEntry;
    GLint linkSuccessful;

    /* Check if we've already cached this program */
    entry = rdata->program_cache.head;
    while (entry)
    {
        if (entry->vertex_shader == vertex && entry->fragment_shader == fragment)
            break;
        entry = entry->next;
    }
    if (entry)
    {
        if (rdata->program_cache.count > 1)
        {
            if (entry->next)
                entry->next->prev = entry->prev;
            if (entry->prev)
                entry->prev->next = entry->next;
            entry->prev = NULL;
            entry->next = rdata->program_cache.head;
            rdata->program_cache.head->prev = entry;
            rdata->program_cache.head = entry;
        }
        return entry;
    }

    /* Create a program cache entry */
    entry = (GLES2_ProgramCacheEntry *)SDL_calloc(1, sizeof(GLES2_ProgramCacheEntry));
    if (!entry)
    {
        SDL_OutOfMemory();
        return NULL;
    }
    entry->vertex_shader = vertex;
    entry->fragment_shader = fragment;
    entry->blend_mode = blendMode;
    
    /* Create the program and link it */
    glGetError();
    entry->id = glCreateProgram();
    glAttachShader(entry->id, vertex->id);
    glAttachShader(entry->id, fragment->id);
    glBindAttribLocation(entry->id, GLES2_ATTRIBUTE_POSITION, "a_position");
    glBindAttribLocation(entry->id, GLES2_ATTRIBUTE_TEXCOORD, "a_texCoord");
    glLinkProgram(entry->id);
    glGetProgramiv(entry->id, GL_LINK_STATUS, &linkSuccessful);
    if (glGetError() != GL_NO_ERROR || !linkSuccessful)
    {
        SDL_SetError("Failed to link shader program");
        glDeleteProgram(entry->id);
        SDL_free(entry);
        return NULL;
    }
    
    /* Predetermine locations of uniform variables */
    entry->uniform_locations[GLES2_UNIFORM_PROJECTION] =
        glGetUniformLocation(entry->id, "u_projection");
    entry->uniform_locations[GLES2_UNIFORM_TEXTURE] =
        glGetUniformLocation(entry->id, "u_texture");
    entry->uniform_locations[GLES2_UNIFORM_MODULATION] =
        glGetUniformLocation(entry->id, "u_modulation");
    entry->uniform_locations[GLES2_UNIFORM_COLOR] =
        glGetUniformLocation(entry->id, "u_color");
    entry->uniform_locations[GLES2_UNIFORM_COLORTABLE] =
        glGetUniformLocation(entry->id, "u_colorTable");

    /* Cache the linked program */
    if (rdata->program_cache.head)
    {
        entry->next = rdata->program_cache.head;
        rdata->program_cache.head->prev = entry;
    }
    else
    {
        rdata->program_cache.tail = entry;
    }
    rdata->program_cache.head = entry;
    ++rdata->program_cache.count;

    /* Increment the refcount of the shaders we're using */
    ++vertex->references;
    ++fragment->references;

    /* Evict the last entry from the cache if we exceed the limit */
    if (rdata->program_cache.count > GLES2_MAX_CACHED_PROGRAMS)
    {
        shaderEntry = rdata->program_cache.tail->vertex_shader;
        if (--shaderEntry->references <= 0)
            GLES2_EvictShader(renderer, shaderEntry);
        shaderEntry = rdata->program_cache.tail->fragment_shader;
        if (--shaderEntry->references <= 0)
            GLES2_EvictShader(renderer, shaderEntry);
        glDeleteProgram(rdata->program_cache.tail->id);
        rdata->program_cache.tail = rdata->program_cache.tail->prev;
        SDL_free(rdata->program_cache.tail->next);
        rdata->program_cache.tail->next = NULL;
        --rdata->program_cache.count;
    }
    return entry;
}

static GLES2_ShaderCacheEntry *
GLES2_CacheShader(SDL_Renderer *renderer, GLES2_ShaderType type, SDL_BlendMode blendMode)
{
    GLES2_DriverContext *rdata = (GLES2_DriverContext *)renderer->driverdata;
    const GLES2_Shader *shader;
    const GLES2_ShaderInstance *instance = NULL;
    GLES2_ShaderCacheEntry *entry = NULL;
    GLint compileSuccessful = GL_FALSE;
    int i, j;

    /* Find the corresponding shader */
    shader = GLES2_GetShader(type, blendMode);
    if (!shader)
    {
        SDL_SetError("No shader matching the requested characteristics was found");
        return NULL;
    }
    
    /* Find a matching shader instance that's supported on this hardware */
    for (i = 0; i < shader->instance_count && !instance; ++i)
    {
        for (j = 0; j < rdata->shader_format_count && !instance; ++j)
        {
            if (!shader->instances)
                continue;
            if (!shader->instances[i])
                continue;
            if (shader->instances[i]->format != rdata->shader_formats[j])
                continue;
            instance = shader->instances[i];
        }
    }
    if (!instance)
    {
        SDL_SetError("The specified shader cannot be loaded on the current platform");
        return NULL;
    }

    /* Check if we've already cached this shader */
    entry = rdata->shader_cache.head;
    while (entry)
    {
        if (entry->instance == instance)
            break;
        entry = entry->next;
    }
    if (entry)
        return entry;

    /* Create a shader cache entry */
    entry = (GLES2_ShaderCacheEntry *)SDL_calloc(1, sizeof(GLES2_ShaderCacheEntry));
    if (!entry)
    {
        SDL_OutOfMemory();
        return NULL;
    }
    entry->type = type;
    entry->instance = instance;

    /* Compile or load the selected shader instance */
    glGetError();
    entry->id = glCreateShader(instance->type);
    if (instance->format == (GLenum)-1)
    {
        glShaderSource(entry->id, 1, (const char **)&instance->data, NULL);
        glCompileShader(entry->id);
        glGetShaderiv(entry->id, GL_COMPILE_STATUS, &compileSuccessful);
    }
    else
    {
        glShaderBinary(1, &entry->id, instance->format, instance->data, instance->length);
        compileSuccessful = GL_TRUE;
    }
    if (glGetError() != GL_NO_ERROR || !compileSuccessful)
    {
        char *info = NULL;
        int length;

        glGetShaderiv(entry->id, GL_INFO_LOG_LENGTH, &length);
        if (length > 0) {
            info = SDL_stack_alloc(char, length);
            if (info) {
                glGetShaderInfoLog(entry->id, length, &length, info);
            }
        }
        if (info) {
            SDL_SetError("Failed to load the shader: %s", info);
            SDL_stack_free(info);
        } else {
            SDL_SetError("Failed to load the shader");
        }
        glDeleteShader(entry->id);
        SDL_free(entry);
        return NULL;
    }

    /* Link the shader entry in at the front of the cache */
    if (rdata->shader_cache.head)
    {
        entry->next = rdata->shader_cache.head;
        rdata->shader_cache.head->prev = entry;
    }
    rdata->shader_cache.head = entry;
    ++rdata->shader_cache.count;
    return entry;
}

static void
GLES2_EvictShader(SDL_Renderer *renderer, GLES2_ShaderCacheEntry *entry)
{
    GLES2_DriverContext *rdata = (GLES2_DriverContext *)renderer->driverdata;

    /* Unlink the shader from the cache */
    if (entry->next)
        entry->next->prev = entry->prev;
    if (entry->prev)
        entry->prev->next = entry->next;
    if (rdata->shader_cache.head == entry)
        rdata->shader_cache.head = entry->next;
    --rdata->shader_cache.count;

    /* Deallocate the shader */
    glDeleteShader(entry->id);
    SDL_free(entry);
}

static int
GLES2_SelectProgram(SDL_Renderer *renderer, GLES2_ImageSource source, SDL_BlendMode blendMode)
{
    GLES2_DriverContext *rdata = (GLES2_DriverContext *)renderer->driverdata;
    GLES2_ShaderCacheEntry *vertex = NULL;
    GLES2_ShaderCacheEntry *fragment = NULL;
    GLES2_ShaderType vtype, ftype;
    GLES2_ProgramCacheEntry *program;

    /* Select an appropriate shader pair for the specified modes */
    vtype = GLES2_SHADER_VERTEX_DEFAULT;
    switch (source)
    {
    case GLES2_IMAGESOURCE_SOLID:
        ftype = GLES2_SHADER_FRAGMENT_SOLID_SRC;
        break;
    case GLES2_IMAGESOURCE_TEXTURE:
        ftype = GLES2_SHADER_FRAGMENT_TEXTURE_SRC;
        break;
    }

    /* Load the requested shaders */
    vertex = GLES2_CacheShader(renderer, vtype, blendMode);
    if (!vertex)
        goto fault;
    fragment = GLES2_CacheShader(renderer, ftype, blendMode);
    if (!fragment)
        goto fault;

    /* Check if we need to change programs at all */
    if (rdata->current_program &&
        rdata->current_program->vertex_shader == vertex &&
        rdata->current_program->fragment_shader == fragment)
        return 0;

    /* Generate a matching program */
    program = GLES2_CacheProgram(renderer, vertex, fragment, blendMode);
    if (!program)
        goto fault;

    /* Select that program in OpenGL */
    glGetError();
    glUseProgram(program->id);
    if (glGetError() != GL_NO_ERROR)
    {
        SDL_SetError("Failed to select program");
        goto fault;
    }

    /* Set the current program */
    rdata->current_program = program;

    /* Activate an orthographic projection */
    if (GLES2_SetOrthographicProjection(renderer) < 0)
        goto fault;

    /* Clean up and return */
    return 0;
fault:
    if (vertex && vertex->references <= 0)
        GLES2_EvictShader(renderer, vertex);
    if (fragment && fragment->references <= 0)
        GLES2_EvictShader(renderer, fragment);
    rdata->current_program = NULL;
    return -1;
}

static int
GLES2_SetOrthographicProjection(SDL_Renderer *renderer)
{
    GLES2_DriverContext *rdata = (GLES2_DriverContext *)renderer->driverdata;
    SDL_Window *window = renderer->window;
    int w, h;
    GLfloat projection[4][4];
    GLuint locProjection;

    /* Get the window width and height */
    SDL_GetWindowSize(window, &w, &h);

    /* Prepare an orthographic projection */
    projection[0][0] = 2.0f / w;
    projection[0][1] = 0.0f;
    projection[0][2] = 0.0f;
    projection[0][3] = 0.0f;
    projection[1][0] = 0.0f;
    projection[1][1] = -2.0f / h;
    projection[1][2] = 0.0f;
    projection[1][3] = 0.0f;
    projection[2][0] = 0.0f;
    projection[2][1] = 0.0f;
    projection[2][2] = 1.0f;
    projection[2][3] = 0.0f;
    projection[3][0] = -1.0f;
    projection[3][1] = 1.0f;
    projection[3][2] = 0.0f;
    projection[3][3] = 1.0f;

    /* Set the projection matrix */
    locProjection = rdata->current_program->uniform_locations[GLES2_UNIFORM_PROJECTION];
    glGetError();
    glUniformMatrix4fv(locProjection, 1, GL_FALSE, (GLfloat *)projection);
    if (glGetError() != GL_NO_ERROR)
    {
        SDL_SetError("Failed to set orthographic projection");
        return -1;
    }
    return 0;
}

/*************************************************************************************************
 * Rendering functions                                                                           *
 *************************************************************************************************/

static const float inv255f = 1.0f / 255.0f;

static int GLES2_RenderClear(SDL_Renderer *renderer);
static int GLES2_RenderDrawPoints(SDL_Renderer *renderer, const SDL_Point *points, int count);
static int GLES2_RenderDrawLines(SDL_Renderer *renderer, const SDL_Point *points, int count);
static int GLES2_RenderFillRects(SDL_Renderer *renderer, const SDL_Rect **rects, int count);
static int GLES2_RenderCopy(SDL_Renderer *renderer, SDL_Texture *texture, const SDL_Rect *srcrect,
                            const SDL_Rect *dstrect);
static void GLES2_RenderPresent(SDL_Renderer *renderer);

static int
GLES2_RenderClear(SDL_Renderer *renderer)
{
    float r = (float)renderer->r * inv255f;
    float g = (float)renderer->g * inv255f;
    float b = (float)renderer->b * inv255f;
    float a = (float)renderer->a * inv255f;

    GLES2_ActivateRenderer(renderer);

    /* Clear the backbuffer with the selected color */
    glClearColor(r, g, b, a);
    glClear(GL_COLOR_BUFFER_BIT);
    return 0;
}

static void
GLES2_SetBlendMode(int blendMode)
{
    switch (blendMode)
    {
    case SDL_BLENDMODE_NONE:
    default:
        glDisable(GL_BLEND);
        break;
    case SDL_BLENDMODE_BLEND:
        glEnable(GL_BLEND);
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
        break;
    case SDL_BLENDMODE_ADD:
        glEnable(GL_BLEND);
        glBlendFunc(GL_SRC_ALPHA, GL_ONE);
        break;
    case SDL_BLENDMODE_MOD:
        glEnable(GL_BLEND);
        glBlendFunc(GL_ZERO, GL_SRC_COLOR);
        break;
    }
}

static int
GLES2_RenderDrawPoints(SDL_Renderer *renderer, const SDL_Point *points, int count)
{
    GLES2_DriverContext *rdata = (GLES2_DriverContext *)renderer->driverdata;
    GLfloat *vertices;
    SDL_BlendMode blendMode;
    int alpha;
    GLuint locColor;
    int idx;

    GLES2_ActivateRenderer(renderer);

    blendMode = renderer->blendMode;
    alpha = renderer->a;

    /* Activate an appropriate shader and set the projection matrix */
    if (GLES2_SelectProgram(renderer, GLES2_IMAGESOURCE_SOLID, blendMode) < 0)
        return -1;

    /* Select the color to draw with */
    locColor = rdata->current_program->uniform_locations[GLES2_UNIFORM_COLOR];
    glGetError();
    glUniform4f(locColor,
                renderer->r * inv255f,
                renderer->g * inv255f,
                renderer->b * inv255f,
                alpha * inv255f);

    /* Configure the correct blend mode */
    GLES2_SetBlendMode(blendMode);

    /* Emit the specified vertices as points */
    vertices = SDL_stack_alloc(GLfloat, count * 2);
    for (idx = 0; idx < count; ++idx)
    {
        GLfloat x = (GLfloat)points[idx].x + 0.5f;
        GLfloat y = (GLfloat)points[idx].y + 0.5f;

        vertices[idx * 2] = x;
        vertices[(idx * 2) + 1] = y;
    }
    glEnableVertexAttribArray(GLES2_ATTRIBUTE_POSITION);
    glVertexAttribPointer(GLES2_ATTRIBUTE_POSITION, 2, GL_FLOAT, GL_FALSE, 0, vertices);
    glDrawArrays(GL_POINTS, 0, count);
    glDisableVertexAttribArray(GLES2_ATTRIBUTE_POSITION);
    SDL_stack_free(vertices);
    if (glGetError() != GL_NO_ERROR)
    {
        SDL_SetError("Failed to render lines");
        return -1;
    }
    return 0;
}

static int
GLES2_RenderDrawLines(SDL_Renderer *renderer, const SDL_Point *points, int count)
{
    GLES2_DriverContext *rdata = (GLES2_DriverContext *)renderer->driverdata;
    GLfloat *vertices;
    SDL_BlendMode blendMode;
    int alpha;
    GLuint locColor;
    int idx;

    GLES2_ActivateRenderer(renderer);

    blendMode = renderer->blendMode;
    alpha = renderer->a;

    /* Activate an appropriate shader and set the projection matrix */
    if (GLES2_SelectProgram(renderer, GLES2_IMAGESOURCE_SOLID, blendMode) < 0)
        return -1;

    /* Select the color to draw with */
    locColor = rdata->current_program->uniform_locations[GLES2_UNIFORM_COLOR];
    glGetError();
    glUniform4f(locColor,
                renderer->r * inv255f,
                renderer->g * inv255f,
                renderer->b * inv255f,
                alpha * inv255f);

    /* Configure the correct blend mode */
    GLES2_SetBlendMode(blendMode);

    /* Emit a line strip including the specified vertices */
    vertices = SDL_stack_alloc(GLfloat, count * 2);
    for (idx = 0; idx < count; ++idx)
    {
        GLfloat x = (GLfloat)points[idx].x + 0.5f;
        GLfloat y = (GLfloat)points[idx].y + 0.5f;

        vertices[idx * 2] = x;
        vertices[(idx * 2) + 1] = y;
    }
    glEnableVertexAttribArray(GLES2_ATTRIBUTE_POSITION);
    glVertexAttribPointer(GLES2_ATTRIBUTE_POSITION, 2, GL_FLOAT, GL_FALSE, 0, vertices);
    glDrawArrays(GL_LINE_STRIP, 0, count);
    glDisableVertexAttribArray(GLES2_ATTRIBUTE_POSITION);
    SDL_stack_free(vertices);
    if (glGetError() != GL_NO_ERROR)
    {
        SDL_SetError("Failed to render lines");
        return -1;
    }
    return 0;
}

static int
GLES2_RenderFillRects(SDL_Renderer *renderer, const SDL_Rect **rects, int count)
{
    GLES2_DriverContext *rdata = (GLES2_DriverContext *)renderer->driverdata;
    GLfloat vertices[8];
    SDL_BlendMode blendMode;
    int alpha;
    GLuint locColor;
    int idx;

    GLES2_ActivateRenderer(renderer);

    blendMode = renderer->blendMode;
    alpha = renderer->a;

    /* Activate an appropriate shader and set the projection matrix */
    if (GLES2_SelectProgram(renderer, GLES2_IMAGESOURCE_SOLID, blendMode) < 0)
        return -1;

    /* Select the color to draw with */
    locColor = rdata->current_program->uniform_locations[GLES2_UNIFORM_COLOR];
    glGetError();
    glUniform4f(locColor,
                renderer->r * inv255f,
                renderer->g * inv255f,
                renderer->b * inv255f,
                alpha * inv255f);

    /* Configure the correct blend mode */
    GLES2_SetBlendMode(blendMode);

    /* Emit a line loop for each rectangle */
    glEnableVertexAttribArray(GLES2_ATTRIBUTE_POSITION);
    for (idx = 0; idx < count; ++idx)
    {
        GLfloat xMin = (GLfloat)rects[idx]->x;
        GLfloat xMax = (GLfloat)(rects[idx]->x + rects[idx]->w);
        GLfloat yMin = (GLfloat)rects[idx]->y;
        GLfloat yMax = (GLfloat)(rects[idx]->y + rects[idx]->h);

        vertices[0] = xMin;
        vertices[1] = yMin;
        vertices[2] = xMax;
        vertices[3] = yMin;
        vertices[4] = xMin;
        vertices[5] = yMax;
        vertices[6] = xMax;
        vertices[7] = yMax;
        glVertexAttribPointer(GLES2_ATTRIBUTE_POSITION, 2, GL_FLOAT, GL_FALSE, 0, vertices);
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
    }
    glDisableVertexAttribArray(GLES2_ATTRIBUTE_POSITION);
    if (glGetError() != GL_NO_ERROR)
    {
        SDL_SetError("Failed to render lines");
        return -1;
    }
    return 0;
}

static int
GLES2_RenderCopy(SDL_Renderer *renderer, SDL_Texture *texture, const SDL_Rect *srcrect,
                 const SDL_Rect *dstrect)
{
    GLES2_DriverContext *rdata = (GLES2_DriverContext *)renderer->driverdata;
    GLES2_TextureData *tdata = (GLES2_TextureData *)texture->driverdata;
    GLES2_ImageSource sourceType;
    SDL_BlendMode blendMode;
    int alpha;
    GLfloat vertices[8];
    GLfloat texCoords[8];
    GLuint locTexture;
    GLuint locModulation;
    GLuint locColorTable;

    GLES2_ActivateRenderer(renderer);

    /* Activate an appropriate shader and set the projection matrix */
    blendMode = texture->blendMode;
    alpha = texture->a;
    sourceType = GLES2_IMAGESOURCE_TEXTURE;
    if (GLES2_SelectProgram(renderer, sourceType, blendMode) < 0)
        return -1;

    /* Select the target texture */
    locTexture = rdata->current_program->uniform_locations[GLES2_UNIFORM_TEXTURE];
    glGetError();
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(tdata->texture_type, tdata->texture);
    glUniform1i(locTexture, 0);

    /* Configure texture blending */
    GLES2_SetBlendMode(blendMode);

    /* Configure color modulation */
    locModulation = rdata->current_program->uniform_locations[GLES2_UNIFORM_MODULATION];
    glUniform4f(locModulation,
                texture->r * inv255f,
                texture->g * inv255f,
                texture->b * inv255f,
                alpha * inv255f);

    /* Emit the textured quad */
    glEnableVertexAttribArray(GLES2_ATTRIBUTE_TEXCOORD);
    glEnableVertexAttribArray(GLES2_ATTRIBUTE_POSITION);
    vertices[0] = (GLfloat)dstrect->x;
    vertices[1] = (GLfloat)dstrect->y;
    vertices[2] = (GLfloat)(dstrect->x + dstrect->w);
    vertices[3] = (GLfloat)dstrect->y;
    vertices[4] = (GLfloat)dstrect->x;
    vertices[5] = (GLfloat)(dstrect->y + dstrect->h);
    vertices[6] = (GLfloat)(dstrect->x + dstrect->w);
    vertices[7] = (GLfloat)(dstrect->y + dstrect->h);
    glVertexAttribPointer(GLES2_ATTRIBUTE_POSITION, 2, GL_FLOAT, GL_FALSE, 0, vertices);
    texCoords[0] = srcrect->x / (GLfloat)texture->w;
    texCoords[1] = srcrect->y / (GLfloat)texture->h;
    texCoords[2] = (srcrect->x + srcrect->w) / (GLfloat)texture->w;
    texCoords[3] = srcrect->y / (GLfloat)texture->h;
    texCoords[4] = srcrect->x / (GLfloat)texture->w;
    texCoords[5] = (srcrect->y + srcrect->h) / (GLfloat)texture->h;
    texCoords[6] = (srcrect->x + srcrect->w) / (GLfloat)texture->w;
    texCoords[7] = (srcrect->y + srcrect->h) / (GLfloat)texture->h;
    glVertexAttribPointer(GLES2_ATTRIBUTE_TEXCOORD, 2, GL_FLOAT, GL_FALSE, 0, texCoords);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
    glDisableVertexAttribArray(GLES2_ATTRIBUTE_POSITION);
    glDisableVertexAttribArray(GLES2_ATTRIBUTE_TEXCOORD);
    if (glGetError() != GL_NO_ERROR)
    {
        SDL_SetError("Failed to render texture");
        return -1;
    }
    return 0;
}

static void
GLES2_RenderPresent(SDL_Renderer *renderer)
{
    GLES2_ActivateRenderer(renderer);

    /* Tell the video driver to swap buffers */
    SDL_GL_SwapWindow(renderer->window);
}

/*************************************************************************************************
 * Renderer instantiation                                                                        *
 *************************************************************************************************/

#define GL_NVIDIA_PLATFORM_BINARY_NV 0x890B

static SDL_Renderer *
GLES2_CreateRenderer(SDL_Window *window, Uint32 flags)
{
    SDL_Renderer *renderer;
    GLES2_DriverContext *rdata;
    GLint nFormats;
#ifndef ZUNE_HD
    GLboolean hasCompiler;
#endif

    /* Create the renderer struct */
    renderer = (SDL_Renderer *)SDL_calloc(1, sizeof(SDL_Renderer));
    if (!renderer) {
        SDL_OutOfMemory();
        return NULL;
    }

    rdata = (GLES2_DriverContext *)SDL_calloc(1, sizeof(GLES2_DriverContext));
    if (!rdata) {
        GLES2_DestroyRenderer(renderer);
        SDL_OutOfMemory();
        return NULL;
    }
    renderer->info = GLES2_RenderDriver.info;
    renderer->window = window;
    renderer->driverdata = rdata;

    renderer->info.flags = SDL_RENDERER_ACCELERATED;

    /* Create an OpenGL ES 2.0 context */
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);

    rdata->context = SDL_GL_CreateContext(window);
    if (!rdata->context)
    {
        GLES2_DestroyRenderer(renderer);
        return NULL;
    }
    if (SDL_GL_MakeCurrent(window, rdata->context) < 0) {
        GLES2_DestroyRenderer(renderer);
        return NULL;
    }

    if (flags & SDL_RENDERER_PRESENTVSYNC) {
        SDL_GL_SetSwapInterval(1);
    } else {
        SDL_GL_SetSwapInterval(0);
    }
    if (SDL_GL_GetSwapInterval() > 0) {
        renderer->info.flags |= SDL_RENDERER_PRESENTVSYNC;
    }

    /* Determine supported shader formats */
    /* HACK: glGetInteger is broken on the Zune HD's compositor, so we just hardcode this */
    glGetError();
#ifdef ZUNE_HD
    nFormats = 1;
#else /* !ZUNE_HD */
    glGetIntegerv(GL_NUM_SHADER_BINARY_FORMATS, &nFormats);
    glGetBooleanv(GL_SHADER_COMPILER, &hasCompiler);
    if (hasCompiler)
        ++nFormats;
#endif /* ZUNE_HD */
    rdata->shader_formats = (GLenum *)SDL_calloc(nFormats, sizeof(GLenum));
    if (!rdata->shader_formats)
    {
        GLES2_DestroyRenderer(renderer);
        SDL_OutOfMemory();
        return NULL;
    }
    rdata->shader_format_count = nFormats;
#ifdef ZUNE_HD
    rdata->shader_formats[0] = GL_NVIDIA_PLATFORM_BINARY_NV;
#else /* !ZUNE_HD */
    glGetIntegerv(GL_SHADER_BINARY_FORMATS, (GLint *)rdata->shader_formats);
    if (glGetError() != GL_NO_ERROR)
    {
        GLES2_DestroyRenderer(renderer);
        SDL_SetError("Failed to query supported shader formats");
        return NULL;
    }
    if (hasCompiler)
        rdata->shader_formats[nFormats - 1] = (GLenum)-1;
#endif /* ZUNE_HD */
	
    rdata->updateSize = SDL_TRUE;

    /* Populate the function pointers for the module */
    renderer->WindowEvent         = &GLES2_WindowEvent;
    renderer->CreateTexture       = &GLES2_CreateTexture;
    renderer->UpdateTexture       = &GLES2_UpdateTexture;
    renderer->LockTexture         = &GLES2_LockTexture;
    renderer->UnlockTexture       = &GLES2_UnlockTexture;
    renderer->SetClipRect         = &GLES2_SetClipRect;
    renderer->RenderClear         = &GLES2_RenderClear;
    renderer->RenderDrawPoints    = &GLES2_RenderDrawPoints;
    renderer->RenderDrawLines     = &GLES2_RenderDrawLines;
    renderer->RenderFillRects     = &GLES2_RenderFillRects;
    renderer->RenderCopy          = &GLES2_RenderCopy;
    renderer->RenderPresent       = &GLES2_RenderPresent;
    renderer->DestroyTexture      = &GLES2_DestroyTexture;
    renderer->DestroyRenderer     = &GLES2_DestroyRenderer;
    return renderer;
}

#endif /* SDL_VIDEO_RENDER_OGL_ES2 && !SDL_RENDER_DISABLED */

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