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Image processing with FBO and GLSL

Started by UsmanWali May 5, 2011 at 8:31 PM 2 replies 4.3k views

Original Post

May 5, 2011 at 8:31 PM

Hello every body.

I am trying to use FBO for multi-pass image filtering (simple blur effect). My 1st shader call working fine (bluring object perfectly) but cannot figure out why 2nd call of shader not working ? (that should make object more blur) I've tried all tutorial after googling but still no luck. Defiantly the problem is in FBO. I am implementing a simple .RAW file texture on a teapot and calling the shader on it.
Here is my code

****** filter.vert
 varying vec2 vTexCoord;
 
 void main(void)
 {
 gl_Position = ftransform();;
 
 vec2 Pos;
 Pos = sign(gl_Vertex.xy); 
 gl_Position = vec4(Pos, 0.0, 1.0); 
 vTexCoord = Pos * 0.5 + 0.5;
 }

****** filter.frag
 
 uniform sampler2D texture1; // the texture with the scene you want to blur
 varying vec2 vTexCoord;
 
 const float blurSize = 1.0/512.0; // I've chosen this size because this will result in that every step will be one pixel wide if the RTScene texture is of size 512x512
 
 void main(void)
 {
 vec4 sum = vec4(0.0);
 
 // blur in y (vertical)
 // take nine samples, with the distance blurSize between them
 sum += texture2D(texture1, vec2(vTexCoord.x - 4.0*blurSize, vTexCoord.y)) * 0.05;
 sum += texture2D(texture1, vec2(vTexCoord.x - 3.0*blurSize, vTexCoord.y)) * 0.09;
 sum += texture2D(texture1, vec2(vTexCoord.x - 2.0*blurSize, vTexCoord.y)) * 0.12;
 sum += texture2D(texture1, vec2(vTexCoord.x - blurSize, vTexCoord.y)) * 0.15;
 sum += texture2D(texture1, vec2(vTexCoord.x, vTexCoord.y)) * 0.16;
 sum += texture2D(texture1, vec2(vTexCoord.x + blurSize, vTexCoord.y)) * 0.15;
 sum += texture2D(texture1, vec2(vTexCoord.x + 2.0*blurSize, vTexCoord.y)) * 0.12;
 sum += texture2D(texture1, vec2(vTexCoord.x + 3.0*blurSize, vTexCoord.y)) * 0.09;
 sum += texture2D(texture1, vec2(vTexCoord.x + 4.0*blurSize, vTexCoord.y)) * 0.05;
 
 gl_FragColor = sum;
 //gl_FragColor = texture2D( texture, vTexCoord );
 }

****** main file
 
 //
 
 #include "stdafx.h"
 #include <iostream>
 #include <stdlib.h>
 #include <stdio.h>
 #include <stdarg.h>
 #include <GL/glew.h>
 #include <GL/gl.h>
 #include <GL/glut.h>
 #include <GL/glext.h>
 #include <math.h>
 #include "shader.h"
 
 #include <string.h>
 #include <windows.h>
 
 Shader shader;
 
 GLdouble angle;
 
 GLfloat xRot = 0;
 GLfloat yRot = 0;
 GLfloat xRotOld = 0;
 GLfloat yRotOld = 0;
 int mouseState = 0;
 int xCenter = 0;
 int yCenter = 0;
 int n;
 int m;
 
 
 //diffuse light color variables
 GLfloat dlr = 1.0;
 GLfloat dlg = 1.0;
 GLfloat dlb = 1.0;
 //ambient light color variables
 GLfloat alr = 0.0;
 GLfloat alg = 0.0;
 GLfloat alb = 0.0;
 //specular light color variables
 GLfloat slr = 0.0;
 GLfloat slg = 1.0;
 GLfloat slb = 0.0;
 //light position variables
 GLfloat lx = 1.0;
 GLfloat ly = 0.2;
 GLfloat lz = 0.5;
 GLfloat lw = 0.0;
 int lastw, lasth;
 static int slices = 25;
 static int stacks = 25;
 
 #define M_ROTATE_XY 1
 
 static GLuint texture;
 GLuint raw_texture_load(const char *filename, int width, int height);
 
 unsigned int fbo; // The frame buffer object
 unsigned int fbo_depth; // The depth buffer for the frame buffer object
 unsigned int fbo_texture; // The texture object to write our frame buffer object to
 int window_width = 500; // The width of our window
 int window_height = 500; // The height of our window
 float rotation_degree = 0.0f; 
 
 void initFrameBufferDepthBuffer(void) {
 
 glGenRenderbuffersEXT(1, &fbo_depth); // Generate one render buffer and store the ID in fbo_depth
 glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, fbo_depth); // Bind the fbo_depth render buffer
 
 glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT, window_width, window_height); // Set the render buffer storage to be a depth component, with a width and height of the window
 
 glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, fbo_depth); // Set the render buffer of this buffer to the depth buffer
 
 glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, 0); // Unbind the render buffer
 }
 
 void initFrameBufferTexture(void) {
 glGenTextures(1, &fbo_texture); // Generate one texture
 glBindTexture(GL_TEXTURE_2D, fbo_texture); // Bind the texture fbo_texture
 
 glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, window_width, window_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL); // Create a standard texture with the width and height of our window
 
 // Setup the basic texture parameters
 glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
 glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
 
 // Unbind the texture
 glBindTexture(GL_TEXTURE_2D, 0);
 }
 
 void initFrameBuffer(void) {
 initFrameBufferDepthBuffer(); // Initialize our frame buffer depth buffer
 
 initFrameBufferTexture(); // Initialize our frame buffer texture
 
 glGenFramebuffersEXT(1, &fbo); // Generate one frame buffer and store the ID in fbo
 glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo); // Bind our frame buffer
 
 glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, fbo_texture, 0); // Attach the texture fbo_texture to the color buffer in our frame buffer
 
 glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, fbo_depth); // Attach the depth buffer fbo_depth to our frame buffer
 
 GLenum status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT); // Check that status of our generated frame buffer
 
 if (status != GL_FRAMEBUFFER_COMPLETE_EXT) // If the frame buffer does not report back as complete
 {
 std::cout << "Couldn't create frame buffer" << std::endl; // Output an error to the console
 exit(0); // Exit the application
 }
 
 glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); // Unbind our frame buffer
 }
 
 
 void init() {
 
 shader.init("filter.vert", "filter.frag");
 
 glClearColor(0, 0, 0, 0);
 angle = 0;
 
 texture = raw_texture_load("01.raw", 256, 256);
 
 
 glEnable(GL_TEXTURE_2D); // Enable texturing so we can bind our frame buffer texture
 glEnable(GL_DEPTH_TEST); // Enable depth testing
 
 initFrameBuffer(); // Create our frame buffer object
 }
 
 void renderTeapotScene(void) {
 glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo); // Bind our frame buffer for rendering
 glPushAttrib(GL_VIEWPORT_BIT | GL_ENABLE_BIT); // Push our glEnable and glViewport states
 glViewport(0, 0, window_width, window_height); // Set the size of the frame buffer view port
 
 glClearColor (0.0f, 0.0f, 1.0f, 1.0f); // Set the clear colour
 glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear the depth and colour buffers
 glLoadIdentity();
 
 glTranslatef(0.0f, 0.0f, -5.0f);
 
 glRotatef(0.0f, 1.0f, 1.0f, 0.0f); // Rotate according to our rotation_degree value
 
 glutSolidTeapot(1.5); // Render a teapot
 
 glPopAttrib(); // Restore our glEnable and glViewport states
 glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); // Unbind our texture
 
 rotation_degree += 0.5f;
 if (rotation_degree > 360.0f)
 rotation_degree = 0.0f;
 }
 
 void anim() {
 angle += 0.1;
 glutPostRedisplay();
 }
 
 
 GLuint raw_texture_load(const char *filename, int width, int height)
 {
 GLuint texture;
 unsigned char *data;
 FILE *file;
 
 // open texture data
 file = fopen(filename, "rb");
 if (file == NULL) return 0;
 else std::cout<<"Done"; 
 // allocate buffer
 data = (unsigned char*) malloc(width * height * 3);
 
 // read texture data
 fread(data, width * height * 3, 1, file);
 fclose(file);
 
 // allocate a texture name
 glGenTextures(1, &texture);
 
 // select our current texture
 glBindTexture(GL_TEXTURE_2D, texture);
 
 // build our texture mipmaps
 gluBuild2DMipmaps(GL_TEXTURE_2D, 3, width, height, GL_RGB, GL_UNSIGNED_BYTE, data);
 
 // free buffer
 free(data);
 
 return texture;
 }
 
 void FreeTexture( GLuint texture ) 
 { 
 glDeleteTextures( 1, &texture ); 
 }
 
 
 void object1 (void) {
 glRotatef(angle, 1.0, 0.0, 0.0); //rotate on the x axis
 glRotatef(angle, 0.0, 1.0, 0.0); //rotate on the y axis
 glRotatef(angle, 0.0, 0.0, 1.0); //rotate on the z axis
 glColor4f(1.0, 1.0, 0.2, 1.0);
 //glScalef(0.2, 0.2, 0.2);
 glutSolidTeapot(1.5);
 //glutSolidTorus(0.5,1.0,50,50);
 }
 
 
 
 void setLighting(void) {
 GLfloat DiffuseLight[] = {dlr, dlg, dlb};
 GLfloat AmbientLight[] = {alr, alg, alb};
 GLfloat SpecularLight[] = {slr, slg, slb};
 
 glLightfv (GL_LIGHT0, GL_DIFFUSE, DiffuseLight);
 glLightfv (GL_LIGHT0, GL_AMBIENT, AmbientLight);
 glLightfv (GL_LIGHT0, GL_SPECULAR, SpecularLight);
 
 GLfloat LightPosition[] = {lx, ly, lz, lw};
 
 glLightfv (GL_LIGHT0, GL_POSITION, LightPosition); 
 //glEnable(GL_LIGHTING);
 //glEnable(GL_LIGHT0);
 
 glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, AmbientLight);
 glMaterialfv(GL_FRONT, GL_SPECULAR, SpecularLight);
 glLightfv(GL_LIGHT0, GL_POSITION, LightPosition);
 }
 
 void display (void) {
 
 setLighting();
 glRotatef(xRot, 1, 0, 0);
 glRotatef(yRot, 0, 1, 0);
 
 renderTeapotScene(); // Render our teapot scene into our frame buffer
 
 glClearColor(1.0f, 0.0f, 0.0f, 1.0f); // Clear the background of our window to red
 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); //Clear the colour buffer (more buffers later on)
 glLoadIdentity(); // Load the Identity Matrix to reset our drawing locations
 
 glTranslatef(0.0f, 0.0f, -2.0f);
 
 // texture is the input, fbo_texture is the output
 //glBindTexture(GL_TEXTURE_2D, texture); // Bind our frame buffer texture
 //glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); //fbo_texture
 //glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT,GL_COLOR_ATTACHMENT0_EXT,GL_TEXTURE_2D,fbo_texture,0);
 
 glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, texture, 0);
 glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, fbo_texture);
 
 
 shader.bind();
 glBindTexture(GL_TEXTURE_2D,texture);
 glActiveTexture(GL_TEXTURE0);
 glBindTexture(GL_TEXTURE_2D, fbo_texture); // Bind our frame buffer texture
 GLuint texloc = glGetUniformLocation(shader.id(), "texture1");
 glUniform1i(texloc,0);
 
 glBegin(GL_QUADS);
 glTexCoord2f(0.0f, 0.0f);
 glVertex3f(-1.0f, -1.0f, 0.0f); // The bottom left corner
 glTexCoord2f(0.0f, 1.0f);
 glVertex3f(-1.0f, 1.0f, 0.0f); // The top left corner
 glTexCoord2f(1.0f, 1.0f);
 glVertex3f(1.0f, 1.0f, 0.0f); // The top right corner
 glTexCoord2f(1.0f, 0.0f);
 glVertex3f(1.0f, -1.0f, 0.0f); // The bottom right corner
 glEnd();
 
 //shader.unbind();
 
 //fbo_texture have the result, texture should be the output in the next iteration
 
 
 shader.bind();
 glBindTexture(GL_TEXTURE_2D,texture);
 glActiveTexture(GL_TEXTURE0);
 glBindTexture(GL_TEXTURE_2D,fbo_texture);
 
 texloc = glGetUniformLocation(shader.id(),"texture1");
 glUniform1i(texloc,0);
 
 glBegin(GL_QUADS);
 glTexCoord2f(0.0f, 0.0f);
 glVertex3f(-1.0f, -1.0f, 0.0f); // The bottom left corner
 glTexCoord2f(0.0f, 1.0f);
 glVertex3f(-1.0f, 1.0f, 0.0f); // The top left corner
 glTexCoord2f(1.0f, 1.0f);
 glVertex3f(1.0f, 1.0f, 0.0f); // The top right corner
 glTexCoord2f(1.0f, 0.0f);
 glVertex3f(1.0f, -1.0f, 0.0f); // The bottom right corner
 glEnd();
 
 shader.unbind();
 glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); 
 glUseProgram(0);
 glBindTexture(GL_TEXTURE_2D, 1); 
 
 glutSwapBuffers();
 }
 
 void reshape (int w, int h) {
 
 lastw = w;
 lasth = h;
 
 glMatrixMode (GL_PROJECTION);
 glLoadIdentity ();
 gluOrtho2D(0.0, (GLfloat) n, 0.0, (GLfloat) m);
 gluPerspective (60, (GLfloat)w / (GLfloat)h, 1.0, 100.0);
 glMatrixMode (GL_MODELVIEW);
 
 }
 
 
 void mouse(int button, int state, int x, int y) {
 xCenter = x;
 yCenter = y;
 
 if (state == GLUT_DOWN) {
 if (button == GLUT_LEFT_BUTTON) {
 mouseState = M_ROTATE_XY;
 xRotOld = xRot;
 yRotOld = yRot;
 }
 } else {
 mouseState = 0;
 }
 }
 
 void motion(int x, int y) {
 if (mouseState == M_ROTATE_XY) {
 xRot = xRotOld + (float)(y - yCenter) / 4.0;
 yRot = yRotOld + (float)(x - xCenter) / 4.0;
 }
 }
 
 int main(int argc, char** argv)
 {
 glutInit(&argc, argv);
 glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);
 glutInitWindowSize(600, 500);
 //glutInitWindowSize(512, 512);
 glutInitWindowPosition(200, 100);
 glutCreateWindow("Lab2");
 glewInit();
 init();
 glutDisplayFunc(display);
 glutIdleFunc(display);
 glutMouseFunc(mouse);
 glutMotionFunc(motion);
 glutIdleFunc(anim);
 glutReshapeFunc(reshape);
 
 reshape(n, m);
 
 glutMainLoop();
 system("pause");
 return 0;
 }

any help would be appreciable

Thnx

karwosts

May 5, 2011 at 10:28 PM

I think you need to clarify exactly what you're trying to do with texture, fbo_texture, etc. for us so we know what your flow is like.

You cannot have a texture bound as a sampler at the same time it is set as a render target, which looks to me like it might be your problem. You can't read and write to a texture in the same pass.

UsmanWali

May 7, 2011 at 2:58 PM

I think you need to clarify exactly what you're trying to do with texture, fbo_texture, etc. for us so we know what your flow is like.

You cannot have a texture bound as a sampler at the same time it is set as a render target, which looks to me like it might be your problem. You can't read and write to a texture in the same pass.

let me short the code and comment it more clearly


 
 #include "stdafx.h"
 #include <iostream>
 #include <stdlib.h>
 #include <stdio.h>
 #include <stdarg.h>
 #include <GL/glew.h>
 #include <GL/gl.h>
 #include <GL/glut.h>
 #include <GL/glext.h>
 #include <math.h>
 #include "shader.h"
 #include <string.h>
 #include <windows.h>
 
 Shader shader;
 
 int n;
 int m;
 
 unsigned int fbo; // The frame buffer object
 unsigned int fbo_depth; // The depth buffer for the frame buffer object
 unsigned int fbo_texture; // The texture object to write our frame buffer object to
 
 static GLuint texture;
 // **************************************************************
 // Here is texture function which simply read the .raw file 
 // im reading this texture just to show a blur effect on an image
 // "texture" will be GL_TEXTURE0
 // **************************************************************
 GLuint raw_texture_load(const char *filename, int width, int height)
 {
 GLuint texture;
 unsigned char *data;
 FILE *file;
 
 // open texture data
 file = fopen(filename, "rb");
 if (file == NULL) return 0;
 else std::cout<<"Done"; 
 // allocate buffer
 data = (unsigned char*) malloc(width * height * 3);
 
 // read texture data
 fread(data, width * height * 3, 1, file);
 fclose(file);
 
 // allocate a texture name
 glGenTextures(1, &texture);
 
 // select our current texture
 glBindTexture(GL_TEXTURE_2D, texture);
 
 // build our texture mipmaps
 gluBuild2DMipmaps(GL_TEXTURE_2D, 3, width, height, GL_RGB, GL_UNSIGNED_BYTE, data);
 
 // free buffer
 free(data);
 
 return texture;
 }
 
 
 // **************************************************************
 // the fbo code got from : http://www.swiftless.com/tutorials/opengl/framebuffer.html 
 // which initializing frame buffer, depth buffer, and fbo_texture
 // "fbo_texture" will be GL_TEXTURE1
 // **************************************************************
 
 void initFrameBufferDepthBuffer(void) {
 
 glGenRenderbuffersEXT(1, &fbo_depth); // Generate one render buffer and store the ID in fbo_depth
 glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, fbo_depth); // Bind the fbo_depth render buffer
 
 glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT, 500, 500); // Set the render buffer storage to be a depth component, with a width and height of the window
 
 glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, fbo_depth); // Set the render buffer of this buffer to the depth buffer
 
 glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, 0); // Unbind the render buffer
 }
 
 void initFrameBufferTexture(void) {
 glGenTextures(1, &fbo_texture); // Generate one texture
 glBindTexture(GL_TEXTURE_2D, fbo_texture); // Bind the texture fbo_texture
 
 glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 500, 500, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL); // Create a standard texture with the width and height of our window
 
 // Setup the basic texture parameters
 glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
 glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
 
 // Unbind the texture
 glBindTexture(GL_TEXTURE_2D, 0);
 }
 
 void initFrameBuffer(void) {
 initFrameBufferDepthBuffer(); // Initialize our frame buffer depth buffer
 
 initFrameBufferTexture(); // Initialize our frame buffer texture
 
 glGenFramebuffersEXT(1, &fbo); // Generate one frame buffer and store the ID in fbo
 glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo); // Bind our frame buffer
 
 glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, fbo_texture, 0); // Attach the texture fbo_texture to the color buffer in our frame buffer
 
 glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, fbo_depth); // Attach the depth buffer fbo_depth to our frame buffer
 
 GLenum status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT); // Check that status of our generated frame buffer
 
 if (status != GL_FRAMEBUFFER_COMPLETE_EXT) // If the frame buffer does not report back as complete
 {
 std::cout << "Couldn't create frame buffer" << std::endl; // Output an error to the console
 exit(0); // Exit the application
 }
 
 glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); // Unbind our frame buffer
 }
 
 
 void init() {
 // reading my shader
 shader.init("filter.vert", "filter.frag");
 
 glClearColor(0, 0, 0, 0);
 
 //reading my texture .raw file
 texture = raw_texture_load("01.raw", 256, 256);
 
 glEnable(GL_TEXTURE_2D); // Enable texturing so we can bind our frame buffer texture
 glEnable(GL_DEPTH_TEST); // Enable depth testing
 
 initFrameBuffer(); // Create our frame buffer object
 }
 
 void renderTeapotScene(void) {
 
 glTranslatef(0.0f, 0.0f, -5.0f);
 glRotatef(0.0f, 1.0f, 1.0f, 0.0f); // Rotate according to our rotation_degree value
 glutSolidTeapot(1.5); // Render a teapot
 
 }
 
 
 void object1 (void) {
 glBegin(GL_QUADS);
 glTexCoord2f(0.0f, 0.0f);
 glVertex3f(-1.0f, -1.0f, 0.0f); // The bottom left corner
 glTexCoord2f(0.0f, 1.0f);
 glVertex3f(-1.0f, 1.0f, 0.0f); // The top left corner
 glTexCoord2f(1.0f, 1.0f);
 glVertex3f(1.0f, 1.0f, 0.0f); // The top right corner
 glTexCoord2f(1.0f, 0.0f);
 glVertex3f(1.0f, -1.0f, 0.0f); // The bottom right corner
 glEnd();
 }
 
 void display (void) {
 
 glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo); // Bind our frame buffer for rendering
 glPushAttrib(GL_VIEWPORT_BIT | GL_ENABLE_BIT); // Push our glEnable and glViewport states
 glViewport(0, 0, 500, 500); // Set the size of the frame buffer view port
 renderTeapotScene(); // Render our teapot scene into our frame buffer
 glPopAttrib(); // Restore our glEnable and glViewport states
 glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); // Unbind our texture
 
 
 
 glClearColor (0.0f, 0.0f, 1.0f, 1.0f); // Set the clear colour
 glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear the depth and colour buffers
 glLoadIdentity();
 
 
 // i assume i have a texture called "texture" which created within texture unit0,
 // a texture called "fbo_texture" which created within texture unit1.
 
 
 glEnable(GL_TEXTURE);
 glActiveTexture(GL_TEXTURE0);
 glBindTexture(GL_TEXTURE_2D,texture);
 //glBindFramebufferEXT(GL_FRAMEBUFFER_EXT,fbo); // i have a framebuffer object called fbo
 glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, fbo_texture, 0);
 
 shader.bind(); //implementing shader 1st time
 glActiveTexture(GL_TEXTURE0);
 glBindTexture(GL_TEXTURE_2D,texture); // i have created the "texture" originally with GL_TEXTURE0
 GLuint texloc = glGetUniformLocation(shader.id(), "texture1");
 glUniform1i(texloc,0); // here 0 means texture unit 0, or GL_TEXTURE0
 
 object1();
 
 //fbo_texture have the result, texture should be the output in the next iteration
 shader.bind(); // 2nd implementation of shader
 glActiveTexture(GL_TEXTURE0); // make texture unit0 active, which have "texture" bind to it,originally
 glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, texture, 0);// switch the destination to "texture".
 
 glActiveTexture(GL_TEXTURE1); // make texture unit 1 active, which have fbo_texture bind to it
 glBindTexture(GL_TEXTURE_2D,fbo_texture);
 
 glUniform1i(texloc,1); // bind fbo_texture to shader as the input
 
 object1();
 
 shader.unbind(); 
 
 
 glDisable(GL_TEXTURE);
 glutSwapBuffers();
 }
 
 void reshape (int w, int h) {
 
 glMatrixMode (GL_PROJECTION);
 glLoadIdentity ();
 gluOrtho2D(0.0, (GLfloat) n, 0.0, (GLfloat) m);
 gluPerspective (60, (GLfloat)w / (GLfloat)h, 1.0, 100.0);
 glMatrixMode (GL_MODELVIEW);
 }
 
 
 int main(int argc, char** argv)
 {
 glutInit(&argc, argv);
 glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);
 glutInitWindowSize(512, 512);
 glutInitWindowPosition(200, 100);
 glutCreateWindow("Lab2");
 glewInit();
 init();
 glutDisplayFunc(display);
 glutIdleFunc(display);
 glutReshapeFunc(reshape);
 reshape(n, m);
 glutMainLoop();
 system("pause");
 return 0;
 }

karwosts

May 7, 2011 at 3:35 PM


 //fbo_texture have the result, texture should be the output in the next iteration
 shader.bind(); // 2nd implementation of shader
 glActiveTexture(GL_TEXTURE0); // make texture unit0 active, which have "texture" bind to it,originally
 glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, texture, 0);// switch the destination to "texture".
 glActiveTexture(GL_TEXTURE1); // make texture unit 1 active, which have fbo_texture bind to it

Yeah it seems like you have the problem I mentioned. In your second drawing pass, you bind texture as a render target, but you never unbind it from sampler 0. If you want to draw to a texture, it cannot be bound as a sampler (or else you get undefined behaviour).

I'm curious why you call glActiveTexture(GL_TEXTURE0) here? It doesn't effect anything that I can see, maybe you don't quite understand what its used for.

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