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POOpenGL ES Framebuffer weird mirroring when drawing
 

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  1. POOpenGL ES Framebuffer weird mirroring when drawing
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    <p>I really can't wrap my mind around this:</p> <p><a href="https://stackoverflow.com/questions/1950232/trying-to-render-to-texture-using-framebuffer-always-results-in-white-texture">Previously</a> I couldn't get Framebuffers to work, but I've got it going now. However, there is this incredibly weird mirroring going on with the texture generated from the framebuffer, and I have no idea why. Basically, I will try to draw a texture at 0,0 using GL_TRIANGLE_FAN, and the texture appears as normal (more or less) in the top right corner, but <em>also</em> appears in the bottom left corner, mirrored. If I fill up most or all of my viewport area with the same texture, the result is an ugly z-fighting overlap.</p> <p>Screenshots will do this more justice.</p> <p>Original image:</p> <p><a href="http://img301.imageshack.us/img301/1518/testsprite.png" rel="nofollow noreferrer">Original http://img301.imageshack.us/img301/1518/testsprite.png</a></p> <p>Drawn 80x80 at (0,0)</p> <p><a href="http://img407.imageshack.us/img407/8339/screenshot20100106at315.png" rel="nofollow noreferrer">80x80 http://img407.imageshack.us/img407/8339/screenshot20100106at315.png</a></p> <p>Drawn 100x180 at (0,0)</p> <p><a href="http://img503.imageshack.us/img503/2584/screenshot20100106at316.png" rel="nofollow noreferrer">100x180 http://img503.imageshack.us/img503/2584/screenshot20100106at316.png</a></p> <p>Drawn 320x480 at (0,0)</p> <p><a href="http://img85.imageshack.us/img85/9172/screenshot20100106at317.png" rel="nofollow noreferrer">320x480 http://img85.imageshack.us/img85/9172/screenshot20100106at317.png</a></p> <p>And here is my code:</p> <p>Set up the view:</p> <pre><code>//Apply the 2D orthographic perspective. glViewport(0,0,320,480); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrthof(0, 320, 480, 0, -10000.0f, 100.0f); //Disable depth testing. glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glDisable(GL_DEPTH_TEST); //Enable vertext and texture coordinate arrays. glEnableClientState(GL_VERTEX_ARRAY); glEnableClientState(GL_TEXTURE_COORD_ARRAY); glShadeModel(GL_SMOOTH); glClearColor(0.5f, 0.5f, 0.5f, 1.0f); glGetError(); // Clear error codes sprite = [Sprite createSpriteFromImage:@"TestSprite.png"]; [sprite retain]; [self createTextureBuffer]; </code></pre> <p>Create the texture buffer.</p> <pre><code>- (void) createTextureBuffer { // generate texture glGenTextures(1, &amp;bufferTexture); glBindTexture(GL_TEXTURE_2D, bufferTexture); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 512, 512, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL); // check if this is right // generate FBO glGenFramebuffersOES(1, &amp;framebuffer); glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer); // associate texture with FBO glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, bufferTexture, 0); // clear texture bind glBindTexture(GL_TEXTURE_2D,0); // check if it worked (probably worth doing :) ) GLuint status = glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES); if (status != GL_FRAMEBUFFER_COMPLETE_OES) { printf("FBO didn't work..."); } } </code></pre> <p>Run the render loop.</p> <pre><code>- (void)drawView { [self drawToTextureBuffer]; // Make sure that you are drawing to the current context [EAGLContext setCurrentContext:context]; //Bind the GLView's buffer. glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer); glViewport(0, 0, 320, 480); //Clear the graphics context. glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); //Push the matrix so we can keep it as it was previously. glPushMatrix(); //Rotate to match landscape mode. glRotatef(90.0, 0, 0, 1); glTranslatef(0.0f, -320.0f, 0.0f); //Store the coordinates/dimensions from the rectangle. float x = 0.0f; float y = 0.0f; float w = 480.0f; float h = 320.0f; // Set up an array of values to use as the sprite vertices. GLfloat vertices[] = { x, y, x, y+h, x+w, y+h, x+w, y }; // Set up an array of values for the texture coordinates. GLfloat texcoords[] = { 0, 0, 0, 1, 1, 1, 0, 1 }; //Render the vertices by pointing to the arrays. glVertexPointer(2, GL_FLOAT, 0, vertices); glTexCoordPointer(2, GL_FLOAT, 0, texcoords); // Set the texture parameters to use a linear filter when minifying. glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); //Enable 2D textures. glEnable(GL_TEXTURE_2D); //Bind this texture. glBindTexture(GL_TEXTURE_2D, bufferTexture); //Finally draw the arrays. glDrawArrays(GL_TRIANGLE_FAN, 0, 4); //Restore the model view matrix to prevent contamination. glPopMatrix(); GLenum err = glGetError(); if (err != GL_NO_ERROR) { NSLog(@"Error on draw. glError: 0x%04X", err); } glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer); [context presentRenderbuffer:GL_RENDERBUFFER_OES]; } </code></pre> <p>On the first pass, the render loop will draw the image into the FBO.</p> <pre><code>- (void)drawToTextureBuffer { if (!bufferWasCreated) { // render to FBO glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer); // set the viewport as the FBO isn't be the same dimension as the screen glViewport(0, 0, 512, 512); glPushMatrix(); //Store the coordinates/dimensions from the rectangle. float x = 0.0f; float y = 0.0f; float w = 320.0f; float h = 480.0f; // Set up an array of values to use as the sprite vertices. GLfloat vertices[] = { x, y, x, y+h, x+w, y+h, x+w, y }; // Set up an array of values for the texture coordinates. GLfloat texcoords[] = { 0, 0, 0, 1, 1, 1, 1, 0 }; //Render the vertices by pointing to the arrays. glVertexPointer(2, GL_FLOAT, 0, vertices); glTexCoordPointer(2, GL_FLOAT, 0, texcoords); // Set the texture parameters to use a linear filter when minifying. glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); //Allow transparency and blending. glEnable(GL_BLEND); glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); //Enable 2D textures. glEnable(GL_TEXTURE_2D); //Bind this texture. glBindTexture(GL_TEXTURE_2D, sprite.texture); //Finally draw the arrays. glDrawArrays(GL_TRIANGLE_FAN, 0, 4); //Restore the model view matrix to prevent contamination. glPopMatrix(); GLenum err = glGetError(); if (err != GL_NO_ERROR) { NSLog(@"Error on draw. glError: 0x%04X", err); } //Unbind this buffer. glBindFramebufferOES(GL_FRAMEBUFFER_OES, 0); bufferWasCreated = YES; } } </code></pre>
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