   reading from texture in shader
  Hi all,I got stuck with the following problem for a few days; I hope, somebody can help me.. Thanks you for any helpMikeFirst, I am writing color-values to a texture attached to a fbo with a fragment-shader. I visualized that, so this step should be correct.Then, I want to read from the texture in another fragment shader and write something out to the color buffer.1. how the texture attached to fbo is set up and drawn (shaders not shown)GLuint avgTex;GLuint avgFB;// generate framebuffer-attachable objectglGenFramebuffersEXT(1, &avgFB);// generate textureglActiveTexture(GL_TEXTURE0);glGenTextures(1, &avgTex);// bind fboglBindFramebufferEXT(GL_FRAMEBUFFER_EXT, avgFB);// initialize textureglBindTexture(GL_TEXTURE_2D, avgTex);glEnable(GL_TEXTURE_2D);glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F_ARB, w, h, 0, GL_RGBA, GL_FLOAT, NULL);[...] 2. how the shaders are set up and texture passed//shaders compiled and attached [...]glUseProgramObjectARB(programObject);// set up texture to read fromglActiveTexture(GL_TEXTURE0);glBindTexture(GL_TEXTURE_2D, avgTex);// set shader parametersGLint locTexAvg;locTexAvg = glGetUniformLocationARB(programObject, "aTex");glUniform1iARB(locTexAvg, 0);3. how the shaders look likevoid main(){gl_TexCoord[0] = gl_MultiTexCoord0;gl_Position = ftransform();}uniform sampler2D aTex;void main(){gl_FragColor = texture2D(aTex, gl_TexCoord[0].xy);} Finally, I visualize that (by simply drawing a quad), which so far stays black. But it should show the color buffer, where I draw to before, right?   
  Wow do you really need to use the 32bit float format? That is going to kill your performance. And I don't see you calling this for your FBOglFramebufferTexture2DEXTto attach a color attachment   ;  Yes, because I am abusing the color texture to store other values. The purpose of the program is to use the parallel power of the gpu for non-standard tasks (i.e. not for displaying).Is the performance decrease really this huge when I use 32bit float? What else do you suggest?I didn't show the whole code how I set up the textures and fbo; here the rest:1. how the texture attached to fbo is set up and drawn (continued)[... {see post above}]// the following options are needed w/ this arg. for correct fbo-setup. why???glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);// attach image to fbglFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, avgTex, 0);CHECK_FRAMEBUFFER_STATUS();// --- draw to the textureglBindTexture(GL_TEXTURE_2D, 0);glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, avgFB);[drawing];  I don't think your glBindTexture() is right with a ZERO.glBindTexture(GL_TEXTURE_2D, avgTex);;  since I am not reading but writing to this texture, this should be right.   ;  I solved the problem.I assumed that I could simply write to each fragment with the shader and forgot to include the glMultiTexCoord2f statements when drawing the quad.   