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POApplying brightness and contrast with OpenGL ES
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  1. POApplying brightness and contrast with OpenGL ES
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    copied!<p>I want to change the brightness <em>and</em> contrast of a texture on the iPhone. I've been looking at the sample provided by apple (<a href="http://developer.apple.com/iphone/library/samplecode/GLImageProcessing/index.html" rel="noreferrer">GLImageProcessing</a>) but it only is able to do one at a time (calling both methods in the sample overwrites the previous result).</p> <p>Brightness works great:</p> <pre><code>glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE); if (brightness &gt;= 1.0f) { glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_ADD); glColor4f(brightness-1, brightness-1, brightness-1, brightness-1); } else { glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_SUBTRACT); glColor4f(1-brightness, 1-brightness, 1-brightness, 1-brightness); } glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_RGB, GL_TEXTURE); glTexEnvi(GL_TEXTURE_ENV, GL_SRC1_RGB, GL_PRIMARY_COLOR); glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_REPLACE); glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_ALPHA, GL_TEXTURE); glDrawArrays(GL_TRIANGLE_FAN, 0, 4); </code></pre> <p>How would i go with adding contrast to the texture after this? Alternatively would it be a better choice to move to OpenGL ES 2.0 and do this with shaders?</p> <p>Here's the code for contrast in the sample from apple:</p> <pre><code>glActiveTexture(GL_TEXTURE0); glVertexPointer (2, GL_FLOAT, sizeof(V2fT2f), &amp;quad[0].x); glTexCoordPointer(2, GL_FLOAT, sizeof(V2fT2f), &amp;quad[0].s); glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE); glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_MODULATE); glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_RGB, GL_TEXTURE); glTexEnvi(GL_TEXTURE_ENV, GL_SRC1_RGB, GL_PRIMARY_COLOR); glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_INTERPOLATE); glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_ALPHA, GL_TEXTURE); glActiveTexture(GL_TEXTURE1); glEnable(GL_TEXTURE_2D); glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE); glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_ADD_SIGNED); glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_RGB, GL_PREVIOUS); glTexEnvi(GL_TEXTURE_ENV, GL_SRC1_RGB, GL_PRIMARY_COLOR); glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_ALPHA); glTexEnvi(GL_TEXTURE_ENV, GL_RGB_SCALE, 2); glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_REPLACE); glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_ALPHA, GL_PREVIOUS); glColor4f(h, h, h, 0.75 - 0.5 * h); // 2x extrapolation validateTexEnv(); glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); // Restore state glDisable(GL_TEXTURE_2D); glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR); glTexEnvi(GL_TEXTURE_ENV, GL_RGB_SCALE, 1); glActiveTexture(GL_TEXTURE0); </code></pre> <p>As you can probably guess my experience with OpenGL (ES) is pretty limited so anything that points me in the right direction is greatly appreciated</p>
 

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