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mitchulese

OpenGL Multiple Images on One Texture

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Hello, I would like to find a method to load several images (from the file system) and apply them to one texture. Currently, I am able to get my application to work by placing one image onto one texture. The problem with this lies in the fact that OpenGL textures are required to be a size of 2n. This can lead to a large waste of memory if I have an image size of 640*480 that requires a texture of 1028*1028. I have considered 2 methods: 1) Create the original image (bmp, jpg, png) with a size of 1028*1028 and placing as many images that I can fit onto it. The following code shows the whole image on the screen: glBegin(GL_TRIANGLE_STRIP); glTexCoord2f( texCoords[0], texCoords[1]); glVertex2i(0, 0); glTexCoord2f( texCoords[2], texCoords[1]); glVertex2i(width, 0); glTexCoord2f( texCoords[0], texCoords[3]); glVertex2i(0, height); glTexCoord2f( texCoords[2], texCoords[3]); glVertex2i(width, height); glEnd(); Once I have this, how then do I determine which image I would actually like to see on the texture? Say I want to see a rectangle of size 50*50 at the location 10, 10. How would I go about doing this? I have tried using glScissor, but with no avail. 2) Programmatically create a large texture with NULL image data and later place seperate image data onto the texture. glGenTextures(1, &texture); glBindTexture(GL_TEXTURE_2D, texture); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); //create the texture glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1024, 1024, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL); ............. //later, pull out image data and replace a spot on the texture glTexSubImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, image->pixels ); This method seems to just produce a blank screen for me. Also, if I can get this method to work, then the viewing of an image from method #1 also comes in to play. Any light on this would be great. If there are any other known methods, I would be grateful to hear of them. Thanks, Dave

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