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POHow do I blend two textures with different co-ordinates in OpenGL ES 2.0 on iPhone?
 

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  1. POHow do I blend two textures with different co-ordinates in OpenGL ES 2.0 on iPhone?
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    <p>I can blend two textures with different blending modes in the fragment shader when both the textures covers the same rectangles. But now my problem is, one texture is a plain rectangle with no rotation and the other texture is another rectangle with a rotation/scale and translation. How do I merge these textures in the way I want? (In the picture)</p> <p>I know how to do this...</p> <p><img src="https://i.stack.imgur.com/CZSa6.png" alt="enter image description here"></p> <p>But not sure how to do this...</p> <p><img src="https://i.stack.imgur.com/2yfyN.png" alt="enter image description here"></p> <p>For blending textures in one rectangle (the first image), I used the following code..</p> <p>Objective C code...</p> <pre><code>- (void) display { [EAGLContext setCurrentContext:context]; glBindFramebuffer(GL_FRAMEBUFFER, targetFBO); glUseProgram(program); glActiveTexture(GL_TEXTURE2); glBindTexture(GL_TEXTURE_2D, textureTop); glActiveTexture(GL_TEXTURE3); glBindTexture(GL_TEXTURE_2D, textureBot); glUniform1i(inputTextureTop, 2); glUniform1i(inputTextureBot, 3); glUniform1f(alphaTop, alpha); glEnable (GL_BLEND); glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); glVertexAttribPointer(position, 2, GL_FLOAT, 0, 0, imageVertices); glVertexAttribPointer(inputTextureCoordinate, 2, GL_FLOAT, 0, 0, textureCoordinates); glClearColor(0.0, 0.0, 0.0, 0.0); glClear(GL_COLOR_BUFFER_BIT); glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); glBindRenderbuffer(GL_RENDERBUFFER, viewRenderbuffer); [context presentRenderbuffer:GL_RENDERBUFFER]; } </code></pre> <p>Vertex shader...</p> <pre><code> attribute vec4 position; attribute vec4 inputTextureCoordinate; varying vec2 textureCoordinate; void main() { gl_Position = position; textureCoordinate = inputTextureCoordinate.xy; } </code></pre> <p>Fragment shader...</p> <pre><code>varying highp vec2 textureCoordinate; uniform sampler2D inputTextureTop; uniform sampler2D inputTextureBot; uniform highp float alphaTop; void main() { lowp vec4 pixelTop = texture2D(inputTextureTop, textureCoordinate); lowp vec4 pixelBot = texture2D(inputTextureBot, textureCoordinate); gl_FragColor = someBlendOperation(pixelTop, pixelBot); } </code></pre>
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    1. COMay be I can do some geometric operation in the fragment shader to get the XY of the top pixel.
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    2. COHi i'm having the same problem, @Max solution doesn't seams to deal with the need to draw the top image at a different size and rotation than the background image, how did you managed to do it?
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