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Craig_jb

glClear alpha on render target

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Hello all,

I am rendering brush strokes in an application to a secondary framebuffer to later render them onto the main framebuffer. However, I am getting weird behavior when clearing the framebuffer. The alpha channel doesn't appear to clear to 0. When I render it, the texture is completely white with alpha of 1.0 it seems. Code below:


// clears the brush strokes from the secondary framebuffer
- (void) clearBrushStrokes
{
glEnable(GL_BLEND);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, renderFrameBuffer);
glClearColor(1.0, 1.0, 1.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
}

// snippet of creation of the render texture
glGenFramebuffersOES(1, &renderFrameBuffer);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, renderFrameBuffer);
glGenTextures(1, &renderTexture);
glBindTexture(GL_TEXTURE_2D, renderTexture);

NSInteger deviceSize = [iChalkDrawingModel sharediChalkDrawingModel].powerOfTwoSize;

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, deviceSize, deviceSize, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, renderTexture, 0);

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