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PORun multiple OpenGL shaders on a CVImageBuffer
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  1. PORun multiple OpenGL shaders on a CVImageBuffer
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    copied!<p>Relating to my previous two questions I've spent a week attempting to figure out how to run multiple shaders against a core video buffer. I <em>know</em> what I need to do but I, frankly, can't get the code to work (pasted below is the original, non ping-pong version).</p> <p>Lacking the Eureka moment I'm now totally stuck :). The code to compile and link the shaders is not shown for brevity. The whole thing renders (successfully - but one shader overwrites the other - so missing the vital step) to a GL compatible layer and theres a UIToolbar underneath which, eventually, will have a button per shader and a button to run all shaders.</p> <p>Thanks,</p> <p>Simon</p> <pre><code>-(void) DrawFrame:(CVImageBufferRef)cameraframe; { int bufferHeight = CVPixelBufferGetHeight(cameraframe); int bufferWidth = CVPixelBufferGetWidth(cameraframe); // Create a new texture from the camera frame data, display that using the shaders glGenTextures(1, &amp;videoFrameTexture); glBindTexture(GL_TEXTURE_2D, videoFrameTexture); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); // Using BGRA extension to pull in video frame data directly glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, bufferWidth, bufferHeight, 0, GL_BGRA, GL_UNSIGNED_BYTE, CVPixelBufferGetBaseAddress(cameraframe)); static const GLfloat squareVertices[] = { -1.0f, -1.0f, 1.0f, -1.0f, -1.0f, 1.0f, 1.0f, 1.0f, }; static const GLfloat textureVertices[] = { 1.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, }; [self setDisplayFramebuffer]; glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, videoFrameTexture); // Update uniform values glUniform1i(uniforms[UNIFORM_VIDEOFRAME], 0); // Update attribute values. glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, 0, 0, squareVertices); glEnableVertexAttribArray(ATTRIB_VERTEX); glVertexAttribPointer(ATTRIB_TEXTUREPOSITON, 2, GL_FLOAT, 0, 0, textureVertices); glEnableVertexAttribArray(ATTRIB_TEXTUREPOSITON); glUseProgram(greyscaleProgram); glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); [self presentFramebuffer]; // Obviously here is where the ping pong starts (assuming correct mods // to the framebuffer setup method below glUseProgram(program); glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); [self presentFramebuffer]; glDeleteTextures(1, &amp;videoFrameTexture); } - (void)setDisplayFramebuffer; { if (context) { [EAGLContext setCurrentContext:context]; if (!viewFramebuffer) { [self createFramebuffers]; } glBindFramebuffer(GL_FRAMEBUFFER, viewFramebuffer); glViewport(0, 0, backingWidth, backingHeight); } } - (BOOL)presentFramebuffer; { BOOL success = FALSE; if (context) { [EAGLContext setCurrentContext:context]; glBindRenderbuffer(GL_RENDERBUFFER, viewRenderbuffer); success = [context presentRenderbuffer:GL_RENDERBUFFER]; } return success; } - (BOOL)createFramebuffers { glEnable(GL_TEXTURE_2D); glDisable(GL_DEPTH_TEST); // Onscreen framebuffer object glGenFramebuffers(1, &amp;viewFramebuffer); glBindFramebuffer(GL_FRAMEBUFFER, viewFramebuffer); // Render buffer for final output glGenRenderbuffers(1, &amp;viewRenderbuffer); glBindRenderbuffer(GL_RENDERBUFFER, viewRenderbuffer); [context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer *)self.layer]; glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &amp;backingWidth); glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &amp;backingHeight); NSLog(@"Backing width: %d, height: %d", backingWidth, backingHeight); glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, viewRenderbuffer); if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) { NSLog(@"Failure with framebuffer generation"); return NO; } return YES; } </code></pre> <p><strong>Edit:</strong> Clarified what is missing</p>
 

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