Hi, I have a few beginners questions!! But first let me show you some code snipet the following code exists in the void COpenGLCanvas::paintGL() method where i am doing some drawings.......... ....... ....... ....... glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbColor); glClearColor(1, 1, 1, 0); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); GLuint sh = shDVR; glUseProgram(sh); glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_3D, volume.txVolume); glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glUniform1i(glGetUniformLocation(sh, "txVolume"), 0); glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, txTf); glUniform1i(glGetUniformLocation(sh, "txTf"), 1); glActiveTexture(GL_TEXTURE2); glBindTexture(GL_TEXTURE_2D, txNoise); glUniform1i(glGetUniformLocation(sh, "txNoise"), 2); glActiveTexture(GL_TEXTURE3); glBindTexture(GL_TEXTURE_2D, txDepth0); glUniform1i(glGetUniformLocation(sh, "txDepth0"), 3); glActiveTexture(GL_TEXTURE4); glBindTexture(GL_TEXTURE_2D, txDepth1); glUniform1i(glGetUniformLocation(sh, "txDepth1"), 4); glActiveTexture(GL_TEXTURE5); glBindTexture(GL_TEXTURE_2D, peel % 2 ? txDepth4 : txDepth2); glTexParameteri(GL_TEXTURE_RECTANGLE_NV, GL_TEXTURE_COMPARE_MODE_ARB, GL_NONE); glUniform1i(glGetUniformLocation(sh, "txDepth2"), 5); glActiveTexture(GL_TEXTURE6); glBindTexture(GL_TEXTURE_2D, peel % 2 ? txDepth5 : txDepth3); glTexParameteri(GL_TEXTURE_RECTANGLE_NV, GL_TEXTURE_COMPARE_MODE_ARB, GL_NONE); glUniform1i(glGetUniformLocation(sh, "txDepth3"), 6); glActiveTexture(GL_TEXTURE7); glBindTexture(GL_TEXTURE_2D, txColor2); glUniform1i(glGetUniformLocation(sh, "txGradient"), 7); glUniform1f(glGetUniformLocation(sh, "zn"), zNear); glUniform1f(glGetUniformLocation(sh, "zf"), zFar); glUniform2f(glGetUniformLocation(sh, "contrast"), contrast.x, contrast.y); glUniform1f(glGetUniformLocation(sh, "minIntensity"), minIntensity); glUniform3f(glGetUniformLocation(sh, "extent"), modelScale.x, modelScale.y, modelScale.z); glUniform1f(glGetUniformLocation(sh, "stepSize"), stepSize); glUniform1i(glGetUniformLocation(sh, "rayDistort"), rayDistort); glUniform1i(glGetUniformLocation(sh, "layer"), layer); glUniform1i(glGetUniformLocation(sh, "maxSamples"), maxSamples); glUniform1f(glGetUniformLocation(sh, "gilThickness"), impreglayerSize); glUniform1i(glGetUniformLocation(sh, "gGThickness"), gGThickness); glBegin(GL_QUADS); glVertex2f(-1, -1); glVertex2f(-1, 1); glVertex2f( 1, 1); glVertex2f( 1, -1); glEnd(); // render image to screen glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); glViewport(0, 0, width(), height()); glUseProgram(0); glClearColor(1, 1, 1, 0.0f); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, txColor0); glEnable(GL_TEXTURE_2D); glBegin(GL_QUADS); glTexCoord2f(0, 0); glVertex2f(-1, -1); glTexCoord2f(0, 1); glVertex2f(-1, 1); glTexCoord2f(1, 1); glVertex2f( 1, 1); glTexCoord2f(1, 0); glVertex2f( 1, -1); glEnd(); ...... ...... ...... this is the code that i recieved from some one and have to make some changes in that. Q1: is my following observations right? "The program makes a frame buffer and passes it to a shader along with many other uniform variables. That shader writes output onto the framebuffer called fbColor. call to 'glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);' prints that output onto the screen. the 'gl_FragColor' statement in the fragment shader in fact writes to the frame buffer and not directly to the fragment!!" Q2 :) My job is to add a second shader here. The idea of my program goes on like this -> The current output from the shader (already implemented) should go to the frame buffer (which i suppose is happening) and that frame buffer should be used as input into a new shader. That new shader modifies the frame buffer somehow and then the updated frame buffer should be displayed. How can I achieve this? how would i access the current frame buffer in the new shader that i will write? do i have to bind all the uniform variables to the new shader as well? how can the new shader be called immediately after the first has finished? is there some quick and simple example or tutorial out on the web?? :( thanks in advance :)