Hello

I'm doing some ping ponging stuff and I am experiencing some weird behaviour with my code. I have 2 shaders which alter the texture and a third one which just displays stuff.

I have a certain number of passes in my program which i can increase and decrease (to make sure that the ping-ponging work). According to my logic, if the number of passes is 0, the color displayed should be black, for 1 pass it should be black, for 2 passes red, for 3 passes yellow, 4 passes orange, ...

However, for 2 passes I'm already getting yellow.

Any help would be very greatly appreciated. Been stuck with that for some time!!!

Thanks

The important part of the code is below:

//some global variables
unsigned char textureArray[4*512*512];

int numberIterations = 0;
GLuint tex_id[2];
GLenum attachmentpoints[] = { GL_COLOR_ATTACHMENT0_EXT, GL_COLOR_ATTACHMENT1_EXT};
int writeTex = 0;
int readTex = 1;
GLuint frameBuffer;
int textureDim = 512;

string shaderPath = "/Users/pascalgrosset/Utah/Research/myVolRender/pingponging/pingponging/";

bool panSc, zoomSc, rotateSc;
float eye[3], lookat[3];

GLint buf_1, buf_2, buf_Out;

GLhandleARB glsl_program1, vertex_shader_1, fragment_shader_1;
GLhandleARB glsl_program2, vertex_shader_2, fragment_shader_2;
GLhandleARB glsl_programOut, vertex_shader_Out, fragment_shader_Out;


// main
int main(int argc, char* argv[])
{
glutInit(&argc, argv);

if (argc > 1)
numberIterations = atoi(argv[1]);

glutInitDisplayMode( GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH);
glutInitWindowPosition( 50, 50);
glutInitWindowSize( windowWidth, windowHeight);

//createGlutMenu();
main_window = glutCreateWindow( "Computer Graphics" );
myInitDisplay(windowWidth, windowHeight);

eye[0] = 0.0; eye[1] = 0.0; eye[2] = 2.0;
lookat[0] = 0.0; lookat[1] = 0.0; lookat[2] = 0.0;

panSc = zoomSc = rotateSc = false;


createShaders(glsl_program1, vertex_shader_1, fragment_shader_1, (shaderPath + string("Shaders/shader.vert")).c_str(), (shaderPath + string("Shaders/fragShader1.frag")).c_str());
createShaders(glsl_program2, vertex_shader_2, fragment_shader_2, (shaderPath + string("Shaders/shader.vert")).c_str(), (shaderPath + string("Shaders/fragShader2.frag")).c_str());
createShaders(glsl_programOut, vertex_shader_Out, fragment_shader_Out, (shaderPath + string("Shaders/shader.vert")).c_str(), (shaderPath + string("Shaders/fragShaderOut.frag")).c_str());

initGL();

// Register some callbacks - basically what function is to be associated to what event
glutDisplayFunc( myDisplay );
glutReshapeFunc( myReshape );
glutIdleFunc( myGlutIdle );
glutKeyboardFunc( myKeyboard );
glutMotionFunc( myMotion );
glutMouseFunc( myMouse );

glutMainLoop();

glDeleteFramebuffersEXT(1, &frameBuffer);

return 0;
}


void myInitDisplay( int width, int height )
{
glClearColor( 0.0f, 0.0f, 0.0f, 0.0f); // This Will Clear The Background and set its Color To Black - 4 params coz of RGBA

glDepthFunc( GL_LESS ); // The Type Of Depth Test To Do
glEnable( GL_DEPTH_TEST ); // Enables Depth Testing
glShadeModel( GL_SMOOTH ); // Enables Smooth Color Shading - GL_SMOOTH or GL_FLAT

glutSetMenu( mainMenuId ); // We have a menu
glutAttachMenu( GLUT_RIGHT_BUTTON ); // Attach the menu to the right mouse button

return;
}


void initGL(){
glEnable(GL_TEXTURE_2D);

for (int i=0; i<(textureDim*textureDim); i++)
textureArray[i*4 +0] = textureArray[i*4 +1] = textureArray[i*4 +2] = textureArray[i*4 +3] = 0;

glGenTextures(2, tex_id);
for (int i=0; i<2; i++){
glBindTexture(GL_TEXTURE_2D, tex_id);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
//NULL means reserve texture memory, but texels are undefined
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, textureDim, textureDim, 0, GL_RGBA, GL_UNSIGNED_BYTE, textureArray);
}


glGenFramebuffersEXT(1, &frameBuffer);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, frameBuffer);

// attach two textures to FBO
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, attachmentpoints[writeTex], GL_TEXTURE_2D, tex_id[writeTex], 0);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, attachmentpoints[readTex], GL_TEXTURE_2D, tex_id[readTex], 0);


GLenum status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT);
if (status == GL_FRAMEBUFFER_COMPLETE_EXT){
// cout << "All Good!!!" << endl;
}
else{
cout << "Error: Binding framebuffer failed" << endl;
exit(0);
}

glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);


initUniformVarsShading1();
initUniformVarsShading2();
initUniformVarsShadingOut();
}


void myDisplay( void )
{
for (int i=0; i<(textureDim*textureDim); i++)
textureArray[i*4 +0] = textureArray[i*4 +1] = textureArray[i*4 +2] = textureArray[i*4 +3] = 0;

writeTex = 0; readTex = 1;

glEnable(GL_TEXTURE_2D);
for (int i=0; i<2; i++){
glBindTexture(GL_TEXTURE_2D, tex_id);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, textureDim, textureDim, 0, GL_RGBA, GL_UNSIGNED_BYTE, textureArray); //NULL);
}


glEnable( GL_DEPTH_TEST );


if (numberIterations == 0){
///////////////////////////
glViewport (0, 0, (GLsizei) textureDim, (GLsizei) textureDim); // set the size of our viewport (window)

glMatrixMode( GL_PROJECTION ); // load the projection matrix; the subsequent transformations are going to affect it
glLoadIdentity(); // initialise the projection matrix before applying the projection matrix

// Specify that we are going to use a perspective projection - changing our projection matrix - NEW!!!!!
gluPerspective(45.0f, (GLfloat)textureDim/(GLfloat)textureDim, 0.1f, 100.0f); //FOV, aspect ratio, near clipping plane, far clipping plane

glMatrixMode( GL_MODELVIEW ); // load the model view matrix - subsequent matrices are going to affect this one
glLoadIdentity();
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
glLoadIdentity();
gluLookAt(eye[0], eye[1], eye[2], lookat[0], lookat[1], lookat[2], 0, 1, 0);
///////////////////////////


glUseProgramObjectARB(glsl_programOut);

glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, tex_id[readTex]);
glUniform1iARB(buf_Out, 0);

glBegin(GL_POLYGON);
glMultiTexCoord2f(GL_TEXTURE0, 0.0, 0.0);
glVertex3f(-0.5, -0.5, -0.5);

glMultiTexCoord2f(GL_TEXTURE0, 1.0, 0.0);
glVertex3f( 0.5, -0.5, -0.5);

glMultiTexCoord2f(GL_TEXTURE0, 1.0, 1.0);
glVertex3f( 0.5, 0.5, -0.5);

glMultiTexCoord2f(GL_TEXTURE0, 0.0, 1.0);
glVertex3f(-0.5, 0.5, -0.5);
glEnd();

glUseProgramObjectARB(0);

}
else{
for (int i=0; i<numberIterations; i++){
//cout << endl << endl << "Pass " << i << " : " << endl;

glPushAttrib(GL_ALL_ATTRIB_BITS);
glPushMatrix();

glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, frameBuffer);
glDrawBuffer(attachmentpoints[writeTex]);

/////////////////
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-0.5,0.5,-0.5,0.5,-0.5,0.5);
glMatrixMode(GL_MODELVIEW);
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
glLoadIdentity();
glViewport(0, 0, textureDim, textureDim);
/////////////////////

if (writeTex == 0){
glUseProgramObjectARB(glsl_program1);

glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, tex_id[readTex]);
glUniform1iARB(buf_1, 0);
}
else{
glUseProgramObjectARB(glsl_program2);

glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, tex_id[readTex]);
glUniform1iARB(buf_2, 0);
}

glNormal3f(0.0, 0.0, -1.0);
glBegin(GL_POLYGON);
glMultiTexCoord2f(GL_TEXTURE0, 0.0, 0.0);
glVertex3f(-0.5, -0.5, -0.5);

glMultiTexCoord2f(GL_TEXTURE0, 1.0, 0.0);
glVertex3f( 0.5, -0.5, -0.5);

glMultiTexCoord2f(GL_TEXTURE0, 1.0, 1.0);
glVertex3f( 0.5, 0.5, -0.5);

glMultiTexCoord2f(GL_TEXTURE0, 0.0, 1.0);
glVertex3f(-0.5, 0.5, -0.5);
glEnd();

glUseProgramObjectARB(0);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);

glPopMatrix();
glPopAttrib();





///////////////////////////
glViewport (0, 0, (GLsizei) textureDim, (GLsizei) textureDim); // set the size of our viewport (window)

glMatrixMode( GL_PROJECTION ); // load the projection matrix; the subsequent transformations are going to affect it
glLoadIdentity(); // initialise the projection matrix before applying the projection matrix

// Specify that we are going to use a perspective projection - changing our projection matrix - NEW!!!!!
gluPerspective(45.0f, (GLfloat)textureDim/(GLfloat)textureDim, 0.1f, 100.0f); //FOV, aspect ratio, near clipping plane, far clipping plane

glMatrixMode( GL_MODELVIEW ); // load the model view matrix - subsequent matrices are going to affect this one
glLoadIdentity();
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
glLoadIdentity();
gluLookAt(eye[0], eye[1], eye[2], lookat[0], lookat[1], lookat[2], 0, 1, 0);
///////////////////////////


glUseProgramObjectARB(glsl_programOut);

glActiveTexture(GL_TEXTURE2);
glBindTexture(GL_TEXTURE_2D, tex_id[readTex]);
glUniform1iARB(buf_Out, 0);

glBegin(GL_POLYGON);
glMultiTexCoord2f(GL_TEXTURE0, 0.0, 0.0);
glVertex3f(-0.5, -0.5, -0.5);

glMultiTexCoord2f(GL_TEXTURE0, 1.0, 0.0);
glVertex3f( 0.5, -0.5, -0.5);

glMultiTexCoord2f(GL_TEXTURE0, 1.0, 1.0);
glVertex3f( 0.5, 0.5, -0.5);

glMultiTexCoord2f(GL_TEXTURE0, 0.0, 1.0);
glVertex3f(-0.5, 0.5, -0.5);
glEnd();

glUseProgramObjectARB(0);

// swap read and write indexes
readTex = 1 - readTex;
writeTex = 1 - writeTex;
}
}

glFlush();
glutSwapBuffers();

return;
}

void initUniformVarsShading1()
{
glUseProgramObjectARB(glsl_program1);

buf_1 = glGetUniformLocationARB(glsl_program1, "tex1");
// glUniform1iARB(buf_1, 0);

glUseProgramObjectARB(0);
}



void initUniformVarsShading2()
{
glUseProgramObjectARB(glsl_program2);

buf_2 = glGetUniformLocationARB(glsl_program2, "tex1");
// glUniform1iARB(buf_2, 0);



glUseProgramObjectARB(0);
}



void initUniformVarsShadingOut()
{
glUseProgramObjectARB(glsl_programOut);

buf_Out = glGetUniformLocationARB(glsl_programOut, "tex1");
// glUniform1iARB(buf_Out, 0);

glUseProgramObjectARB(0);
}


//fragShader1
uniform sampler2D tex1;
varying vec4 vVertex;
void main(){
vec4 colorBuf = texture2D(tex1, gl_TexCoord[0].xy);
gl_FragData[0] = vec4(0.75,0.0,0.0, 0.25) + colorBuf;
}

//fragShader2
uniform sampler2D tex1;
varying vec4 vVertex;
void main(){
vec4 colorBuf = texture2D(tex1, gl_TexCoord[0].xy);
if (colorBuf.a < 0.5)
gl_FragData[0] = vec4(0.0,0.75,0.0, 0.25) + colorBuf;
else
gl_FragData[0] = vec4(0.0,0.0,0.4, 0.25) + colorBuf;
}

//fragShaderOut
uniform sampler2D tex1;
varying vec4 vVertex;
void main(){
vec4 color = texture2D(tex1, gl_TexCoord[0].xy);
gl_FragColor = color;
}

//shader.vert
varying vec4 vVertex;
void main(){
gl_TexCoord[0] = gl_MultiTexCoord0.xyzw;
vVertex = vec4(gl_ModelViewProjectionMatrix * gl_Vertex);
gl_Position = ftransform();
}[/quote]

Got the answer!. There was a typo in my code

glActiveTexture(GL_TEXTURE2); glBindTexture(GL_TEXTURE_2D, tex_id[readTex]); glUniform1iARB(buf_Out, 0);
glActiveTexture(GL_TEXTURE2); should have been glActiveTexture(GL_TEXTURE0);