# HG changeset patch
# User Sam Lantinga <slouken@libsdl.org>
# Date 1258787661 0
# Node ID 7bdc10624cba3f8f38e2209b12f2bf665d956e90
# Parent  fdd2f2e9cd971c97a5dba147a55be7604c73c3c1
This is terrible, but the OpenGL standard says that lines are half open, which means that one endpoint is not covered so adjoining lines don't overlap.  It also doesn't define which end is open, and indeed Mac OS X and Linux differ.  Mac OS X seems to leave the second endpoint open, but Linux uses the right-most endpoint for x major lines and the bottom-most endpoint for y major lines.

diff -r fdd2f2e9cd97 -r 7bdc10624cba src/video/SDL_renderer_gl.c
--- a/src/video/SDL_renderer_gl.c	Sat Nov 21 06:34:43 2009 +0000
+++ b/src/video/SDL_renderer_gl.c	Sat Nov 21 07:14:21 2009 +0000
@@ -1150,22 +1150,20 @@
                     (GLfloat) renderer->b * inv255f,
                     (GLfloat) renderer->a * inv255f);
 
+    /* The line is half open, so we need tiny segments at the endpoints
+     * so that we guarantee coverage of the beginning and final pixels.
+     * http://www.opengl.org/documentation/specs/version1.1/glspec1.1/node47.html
+     */
     data->glBegin(GL_LINES);
+    /* Ensure coverage of the first point */
+    data->glVertex2f(0.1f + x1, 0.1f + y1);
+    data->glVertex2f(0.5f + x1, 0.5f + y1);
+    /* Draw the requested line */
     data->glVertex2f(0.5f + x1, 0.5f + y1);
     data->glVertex2f(0.5f + x2, 0.5f + y2);
-    data->glEnd();
-
-    /* For some reason the rightmost or lowest endpoint is skipped */
-    data->glBegin(GL_POINTS);
-    if (x1 > x2) {
-        data->glVertex2f(0.5f + x1, 0.5f + y1);
-    } else if (x2 > x1) {
-        data->glVertex2f(0.5f + x2, 0.5f + y2);
-    } else if (y1 > y2) {
-        data->glVertex2f(0.5f + x1, 0.5f + y1);
-    } else if (y2 > y1) {
-        data->glVertex2f(0.5f + x2, 0.5f + y2);
-    }
+    /* Ensure coverage of the second point */
+    data->glVertex2f(0.5f + x2, 0.5f + y2);
+    data->glVertex2f(0.9f + x2, 0.9f + y2);
     data->glEnd();
 
     return 0;