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1 <HTML
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2 ><HEAD
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3 ><TITLE
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4 >SDL_SetAlpha</TITLE
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5 ><META
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6 NAME="GENERATOR"
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7 CONTENT="Modular DocBook HTML Stylesheet Version 1.61
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16 TITLE="SDL_SetColorKey"
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17 HREF="sdlsetcolorkey.html"><LINK
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27 ALINK="#ff0000"
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28 ><DIV
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29 CLASS="NAVHEADER"
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30 ><TABLE
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32 BORDER="0"
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33 CELLPADDING="0"
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34 CELLSPACING="0"
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35 ><TR
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36 ><TH
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37 COLSPAN="3"
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38 ALIGN="center"
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39 >SDL Library Documentation</TH
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40 ></TR
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41 ><TR
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42 ><TD
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43 WIDTH="10%"
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44 ALIGN="left"
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45 VALIGN="bottom"
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46 ><A
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47 HREF="sdlsetcolorkey.html"
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48 >Prev</A
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49 ></TD
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50 ><TD
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51 WIDTH="80%"
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52 ALIGN="center"
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53 VALIGN="bottom"
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54 ></TD
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55 ><TD
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56 WIDTH="10%"
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57 ALIGN="right"
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58 VALIGN="bottom"
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59 ><A
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60 HREF="sdlsetcliprect.html"
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61 >Next</A
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62 ></TD
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63 ></TR
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64 ></TABLE
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65 ><HR
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66 ALIGN="LEFT"
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67 WIDTH="100%"></DIV
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68 ><H1
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69 ><A
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70 NAME="SDLSETALPHA"
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71 >SDL_SetAlpha</A
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72 ></H1
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73 ><DIV
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74 CLASS="REFNAMEDIV"
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75 ><A
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76 NAME="AEN1612"
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77 ></A
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78 ><H2
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79 >Name</H2
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80 >SDL_SetAlpha -- Adjust the alpha properties of a surface</DIV
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81 ><DIV
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82 CLASS="REFSYNOPSISDIV"
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83 ><A
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84 NAME="AEN1615"
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85 ></A
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86 ><H2
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87 >Synopsis</H2
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88 ><DIV
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89 CLASS="FUNCSYNOPSIS"
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90 ><A
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91 NAME="AEN1616"
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92 ></A
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93 ><P
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94 ></P
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95 ><PRE
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96 CLASS="FUNCSYNOPSISINFO"
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97 >#include "SDL.h"</PRE
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98 ><P
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99 ><CODE
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100 ><CODE
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101 CLASS="FUNCDEF"
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102 >int <B
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103 CLASS="FSFUNC"
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104 >SDL_SetAlpha</B
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105 ></CODE
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106 >(SDL_Surface *surface, Uint32 flag, Uint8 alpha);</CODE
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107 ></P
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108 ><P
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109 ></P
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110 ></DIV
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111 ></DIV
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112 ><DIV
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113 CLASS="REFSECT1"
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114 ><A
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115 NAME="AEN1622"
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116 ></A
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117 ><H2
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118 >Description</H2
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119 ><DIV
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120 CLASS="NOTE"
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121 ><BLOCKQUOTE
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122 CLASS="NOTE"
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123 ><P
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124 ><B
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125 >Note: </B
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126 >This function and the semantics of SDL alpha blending have changed since version 1.1.4. Up until version 1.1.5, an alpha value of 0 was considered opaque and a value of 255 was considered transparent. This has now been inverted: 0 (<TT
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127 CLASS="LITERAL"
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128 >SDL_ALPHA_TRANSPARENT</TT
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129 >) is now considered transparent and 255 (<TT
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130 CLASS="LITERAL"
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131 >SDL_ALPHA_OPAQUE</TT
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132 >) is now considered opaque.</P
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133 ></BLOCKQUOTE
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134 ></DIV
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135 ><P
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136 ><TT
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137 CLASS="FUNCTION"
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138 >SDL_SetAlpha</TT
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139 > is used for setting the per-surface alpha and/or enabling and disabling per-pixel alpha blending.</P
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140 ><P
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141 >The <TT
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142 CLASS="PARAMETER"
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143 ><I
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144 >surface</I
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145 ></TT
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146 > parameter specifies which surface whose alpha attributes you wish to adjust. <TT
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147 CLASS="PARAMETER"
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148 ><I
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149 >flags</I
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150 ></TT
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151 > is used to specify whether alpha blending should be used (<TT
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152 CLASS="LITERAL"
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153 >SDL_SRCALPHA</TT
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154 >) and whether the surface should use RLE acceleration for blitting (<TT
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155 CLASS="LITERAL"
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156 >SDL_RLEACCEL</TT
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157 >). <TT
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158 CLASS="PARAMETER"
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159 ><I
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160 >flags</I
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161 ></TT
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162 > can be an OR'd combination of these two options, one of these options or 0. If <TT
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163 CLASS="LITERAL"
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164 >SDL_SRCALPHA</TT
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165 > is not passed as a flag then all alpha information is ignored when blitting the surface. The <TT
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166 CLASS="PARAMETER"
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167 ><I
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168 >alpha</I
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169 ></TT
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170 > parameter is the per-surface alpha value, a surface need not have an alpha channel to use per-surface alpha and blitting can still be accelerated with <TT
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171 CLASS="LITERAL"
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172 >SDL_RLEACCEL</TT
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173 >. Setting the per-surface alpha value to 0 disables per-surface alpha blending.</P
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174 ><DIV
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175 CLASS="NOTE"
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176 ><BLOCKQUOTE
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177 CLASS="NOTE"
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178 ><P
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179 ><B
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180 >Note: </B
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181 >The per-surface alpha value of 128 is considered a special case and is optimised, so it's much faster than other per-surface values.</P
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182 ></BLOCKQUOTE
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183 ></DIV
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184 ><P
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185 >Alpha effects surface blitting in the following ways:</P
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186 ><DIV
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187 CLASS="INFORMALTABLE"
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188 ><A
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189 NAME="AEN1642"
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190 ></A
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191 ><P
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192 ></P
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193 ><TABLE
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194 BORDER="0"
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195 CLASS="CALSTABLE"
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196 ><TBODY
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197 ><TR
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198 ><TD
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199 ALIGN="LEFT"
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200 VALIGN="TOP"
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201 >RGBA->RGB with <TT
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202 CLASS="LITERAL"
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203 >SDL_SRCALPHA</TT
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204 ></TD
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205 ><TD
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206 ALIGN="LEFT"
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207 VALIGN="TOP"
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208 ><P
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209 >The source is alpha-blended with the destination, using the alpha channel. <TT
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210 CLASS="LITERAL"
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211 >SDL_SRCCOLORKEY</TT
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212 > and the per-surface alpha are ignored.</P
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213 ></TD
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214 ></TR
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215 ><TR
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216 ><TD
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217 ALIGN="LEFT"
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218 VALIGN="TOP"
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219 >RGBA->RGB without <TT
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220 CLASS="LITERAL"
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221 >SDL_SRCALPHA</TT
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222 ></TD
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223 ><TD
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224 ALIGN="LEFT"
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225 VALIGN="TOP"
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226 ><P
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227 >The RGB data is copied from the source. The source alpha channel and the per-surface alpha value are ignored.</P
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228 ></TD
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229 ></TR
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230 ><TR
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231 ><TD
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232 ALIGN="LEFT"
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233 VALIGN="TOP"
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234 >RGB->RGBA with <TT
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235 CLASS="LITERAL"
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236 >SDL_SRCALPHA</TT
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237 ></TD
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238 ><TD
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239 ALIGN="LEFT"
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240 VALIGN="TOP"
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241 ><P
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242 >The source is alpha-blended with the destination using the per-surface alpha value. If <TT
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243 CLASS="LITERAL"
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244 >SDL_SRCCOLORKEY</TT
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245 >literal> is set, only the pixels not matching the colorkey value are copied.</P
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246 ></TD
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247 ></TR
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248 ><TR
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249 ><TD
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250 ALIGN="LEFT"
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251 VALIGN="TOP"
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252 >RGB->RGBA without <TT
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253 CLASS="LITERAL"
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254 >SDL_SRCALPHA</TT
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255 ></TD
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256 ><TD
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257 ALIGN="LEFT"
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258 VALIGN="TOP"
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259 ><P
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260 >The RGB data is copied from the source and the destination alpha is zero to opaque. If <TT
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261 CLASS="LITERAL"
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262 >SDL_SRCCOLORKEY</TT
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263 > is set, only the pixels not matching the colorkey value are copied.</P
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264 ></TD
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265 ></TR
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266 ><TR
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267 ><TD
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268 ALIGN="LEFT"
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269 VALIGN="TOP"
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270 >RGBA->RGBA with <TT
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271 CLASS="LITERAL"
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272 >SDL_SRCALPHA</TT
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273 ></TD
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274 ><TD
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275 ALIGN="LEFT"
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276 VALIGN="TOP"
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277 ><P
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278 >The source is alpha-blended with the destination using the source alpha channel. The alpha channel in the destination surface is left untouched. <TT
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279 CLASS="LITERAL"
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280 >SDL_SRCCOLORKEY</TT
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281 > is ignored.</P
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282 ></TD
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283 ></TR
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284 ><TR
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285 ><TD
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286 ALIGN="LEFT"
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287 VALIGN="TOP"
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288 >RGBA->RGBA without <TT
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289 CLASS="LITERAL"
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290 >SDL_SRCALPHA</TT
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291 ></TD
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292 ><TD
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293 ALIGN="LEFT"
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294 VALIGN="TOP"
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295 ><P
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296 >The RGBA data is copied to the destination surface. If <TT
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297 CLASS="LITERAL"
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298 >SDL_SRCCOLORKEY</TT
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299 > is set, only the pixels not matching the colorkey value are copied.</P
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300 ></TD
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301 ></TR
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302 ><TR
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303 ><TD
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304 ALIGN="LEFT"
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305 VALIGN="TOP"
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306 >RGB->RGB with <TT
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307 CLASS="LITERAL"
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308 >SDL_SRCALPHA</TT
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309 ></TD
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310 ><TD
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311 ALIGN="LEFT"
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312 VALIGN="TOP"
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313 ><P
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314 >The source is alpha-blended with the destination using the per-surface alpha value. If <TT
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315 CLASS="LITERAL"
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316 >SDL_SRCCOLORKEY</TT
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317 > is set, only the pixels not matching the colorkey value are copied.</P
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318 ></TD
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319 ></TR
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320 ><TR
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321 ><TD
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322 ALIGN="LEFT"
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323 VALIGN="TOP"
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324 >RGB->RGB without <TT
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325 CLASS="LITERAL"
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326 >SDL_SRCALPHA</TT
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327 ></TD
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328 ><TD
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329 ALIGN="LEFT"
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330 VALIGN="TOP"
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331 ><P
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332 >The RGB data is copied from the source. If <TT
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333 CLASS="LITERAL"
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334 >SDL_SRCCOLORKEY</TT
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335 > is set, only the pixels not matching the colorkey value are copied.</P
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336 ></TD
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337 ></TR
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338 ></TBODY
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339 ></TABLE
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340 ><P
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341 ></P
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342 ></DIV
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343 ></DIV
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344 ><DIV
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345 CLASS="REFSECT1"
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346 ><A
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347 NAME="AEN1692"
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348 ></A
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349 ><H2
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350 >See Also</H2
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351 ><P
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352 ><A
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353 HREF="sdlmaprgba.html"
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354 ><TT
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355 CLASS="FUNCTION"
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356 >SDL_MapRGBA</TT
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357 ></A
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358 >,
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359 <A
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360 HREF="sdlgetrgba.html"
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361 ><TT
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362 CLASS="FUNCTION"
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363 >SDL_GetRGBA</TT
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364 ></A
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365 >,
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366 <A
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367 HREF="sdldisplayformatalpha.html"
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368 ><TT
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369 CLASS="FUNCTION"
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370 >SDL_DisplayFormatAlpha</TT
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371 ></A
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372 >,
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373 <A
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374 HREF="sdlblitsurface.html"
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375 ><TT
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376 CLASS="FUNCTION"
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377 >SDL_BlitSurface</TT
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378 ></A
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379 ></P
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380 ></DIV
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381 ><DIV
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382 CLASS="NAVFOOTER"
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383 ><HR
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384 ALIGN="LEFT"
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385 WIDTH="100%"><TABLE
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386 WIDTH="100%"
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387 BORDER="0"
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388 CELLPADDING="0"
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389 CELLSPACING="0"
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390 ><TR
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391 ><TD
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392 WIDTH="33%"
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393 ALIGN="left"
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394 VALIGN="top"
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395 ><A
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396 HREF="sdlsetcolorkey.html"
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397 >Prev</A
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398 ></TD
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399 ><TD
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400 WIDTH="34%"
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401 ALIGN="center"
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402 VALIGN="top"
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403 ><A
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404 HREF="index.html"
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405 >Home</A
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406 ></TD
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407 ><TD
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408 WIDTH="33%"
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409 ALIGN="right"
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410 VALIGN="top"
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411 ><A
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412 HREF="sdlsetcliprect.html"
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413 >Next</A
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414 ></TD
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415 ></TR
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416 ><TR
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417 ><TD
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418 WIDTH="33%"
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419 ALIGN="left"
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420 VALIGN="top"
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421 >SDL_SetColorKey</TD
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422 ><TD
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423 WIDTH="34%"
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424 ALIGN="center"
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425 VALIGN="top"
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426 ><A
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427 HREF="video.html"
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428 >Up</A
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429 ></TD
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430 ><TD
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431 WIDTH="33%"
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432 ALIGN="right"
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433 VALIGN="top"
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434 >SDL_SetClipRect</TD
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435 ></TR
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436 ></TABLE
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437 ></DIV
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438 ></BODY
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439 ></HTML
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440 > |
