OpenGL Stereo: alternating between left and right textures - c++

Question

I am working with openGL quad buffer to render stereo 3D images (and I am very new to openGL).
I came across a question on how to define the output texture for each back buffer, which I supose is done in the fragment buffer by defining the output color (corresponding to a specified texture).
This is the code I am using for the shader sources:
// Shader sources
const GLchar* vertexSource =
"#version 150 core\n"
"in vec2 position;"
"in vec3 color;"
"in vec2 texcoord;"
"out vec3 Color;"
"out vec2 Texcoord;"
"void main() {"
" Color = color;"
" Texcoord = texcoord;"
" gl_Position = vec4(position, 0.0, 1.0);"
"}"; // Vertex buffer source
const GLchar* fragmentSource =
"#version 150 core\n"
"in vec3 Color;"
"in vec2 Texcoord;"
"out vec4 outColor;"
"uniform sampler2D texRight;"
"uniform sampler2D texLeft;"
"void main() {"
" outColor = texture(texRight, Texcoord);"
" outColor = texture(texLeft, Texcoord);"
"}"; // Fragment buffer source
This is the code I am using to fill the back buffers, that I use in the display function for the freeglut context window.
// Clear Buffers
glDrawBuffer(GL_BACK);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glClearColor(0.0f, 0.0f, 0.0f,1.0f);
cudaGLMapBufferObject((void**)d_glpointer, pbo);
cudaGLMapBufferObject((void**)d_glpointer, pbo_Right);
//...
// Unmap buffer object
cudaGLUnmapBufferObject(pbo);
glBindBuffer( GL_PIXEL_UNPACK_BUFFER, pbo);
glDrawBuffer(GL_BACK_LEFT);
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, texturesID[1]);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, image_width, image_height, 0, GL_RGBA, GL_UNSIGNED_BYTE,NULL); // NULL specifies that the image is in memory
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glUniform1i(glGetUniformLocation(shaderProgram, "texLeft"), 1);
// Draw a rectangle from the 2 triangles using 6 indices
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
// Unmap buffer object
cudaGLUnmapBufferObject(pbo_Right);
glBindBuffer( GL_PIXEL_UNPACK_BUFFER, pbo_Right);
// Draw Back Buffers
glDrawBuffer(GL_BACK_RIGHT);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texturesID[0]);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, image_width, image_height, 0, GL_RGBA, GL_UNSIGNED_BYTE,NULL); // NULL specifies that the image is in memory
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glUniform1i(glGetUniformLocation(shaderProgram, "texRight"), 0);
// Draw a rectangle from the 2 triangles using 6 indices
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
// Swap buffers
glutSwapBuffers();
By using this code I am able to see only the last outcolor defined, but I was not able to figure out a functional way to choose between the outColor definition depending on the buffer I am using.
I am using Cuda to put the images in memory, but the problem doesn't seem related to this mapping, since I am always able to see the image associated with texture defined last in the shader's outcolor.
I'll appreciate some help on figuring this out.
Edit 1:
I added a counter to the shader that verifies if the frame count (texCount) is even or odd. Although, I have no output image now.
#version 150 core
in vec3 Color;
in vec2 Texcoord;
out vec4 outColor;
uniform sampler2D texRight;
uniform sampler2D texLeft;
uniform int texCount=1;
void main() {
if (texCount%2){ // if texCount division by two is exact then this is false
outColor = texture(texLeft, Texcoord);
}else{
outColor = texture(texRight, Texcoord);
}
texCount++;
}

Answer 1

I think the following should work.
The new fragment shader:
#version 150 core in vec3 Color;
in vec2 Texcoord;
out vec4 outColor;
uniform sampler2D texIndex;
void main() {
outColor = texture(texIndex, Texcoord);
}
Then replace ”texLeft” and ”texRight” in your code by ”texIndex”.
Note that you shouldn't have to upload the textures at each frame if they are static. Ideally, you would put all the commands that need to be executed only once in a setup function, which you would execute only when the OS notify a window reshape.