2 Textures, 1 Shader - OpenGL ES 2.0

Question

ES 2.0 newbie here. I'm currently trying to make some 3D interlaced images from stereo images with ES 2.0 and the PowerVR SDK. I can output one image texture fine, but when I try to output the second one, I seem to be overwriting the first. So, my question is, given the fragment shader below, can I use it to draw two textures, or can the sampler2d uniform only be bound to one texture unit? Here's the fragment shader (taken from the PowerVR "training course" sample programs):

    uniform sampler2D sampler2d;\
    varying mediump vec2    myTexCoord;\
    void main (void)\
    {\
        gl_FragColor = texture2D(sampler2d,myTexCoord);\
    }";

And here's how I am loading the image textures into the shader:

//LEFT IMAGE
glActiveTexture(GL_TEXTURE0);
glGenTextures(1, &m_uiTexture_left);                                    
glBindTexture(GL_TEXTURE_2D, m_uiTexture_left);
glUniform1i(glGetUniformLocation(m_uiProgramObject, "sampler2d"), 0);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, pwr2Width, pwr2Height,0, GL_RGB, GL_UNSIGNED_BYTE, xImageL); 
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
GLfloat afVertices[30] = {0.0};
genVertices(afVertices);
glGenBuffers(1, &m_ui32Vbo_leftimage);                                  
m_ui32VertexStride = 5 * sizeof(GLfloat); // 3 floats for the pos, 2 for the UVs
glBindBuffer(GL_ARRAY_BUFFER, m_ui32Vbo_leftimage);
glBufferData(GL_ARRAY_BUFFER, 6 * m_ui32VertexStride, afVertices, GL_STATIC_DRAW);  
glBindBuffer(GL_ARRAY_BUFFER, 0);

//RIGHT IMAGE
glActiveTexture(GL_TEXTURE1);
glGenTextures(1, &m_uiTexture_right);                                   
glBindTexture(GL_TEXTURE_2D, m_uiTexture_right);
glUniform1i(glGetUniformLocation(m_uiProgramObject, "sampler2d"), 1);   
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, pwr2Width, pwr2Height,0, GL_RGB, GL_UNSIGNED_BYTE, xImageR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glGenBuffers(1, &m_ui32Vbo_rightimage);                     
m_ui32VertexStride = 5 * sizeof(GLfloat); // 3 floats for the pos, 2 for the UVs
glBindBuffer(GL_ARRAY_BUFFER, m_ui32Vbo_rightimage);
glBufferData(GL_ARRAY_BUFFER, 6 * m_ui32VertexStride, afVertices, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);

So, is this code just overwriting the sampler2d uniform? Do I need another uniform or shader for the second image?

Welp, this is embarrassing... I think I've solved it. After reading this: opentk.com/node/2559, I did as the poster "Profet" mentioned and moved the glUniform1i() calls down to my render function, so technically I am still overwriting the value in sampler2d (afaik), but by the time I make the second glUniform1i() call and overwrite it, I've already drawn the first image. Maybe this will help someone having the same issue, as I did a fair amount of Googling myself and found it hard to find something relevant. — Stereoscopic
can you please put the answer so that no one spends time trying a solution for it :) — Maurizio Benedetti
Write an answer instead of a comment? Sure, I can do that. (I'm new to the site, I wasn't sure what the etiquette was with regards to answering my own question) — Stereoscopic

Stereoscopic Stereoscopic · Accepted Answer · 2012-02-14T10:53:10

Ok, so as I mentioned in the comment above, I eventually found the answer here: http://www.opentk.com/node/2559. As mentioned by the user "Profet" on that forum, one way to re-use the fragment shader is to move the glUniform1i() calls down to the render function, i.e. call glUniform1i() to pass the first texture to the shader, call glDraw (draw your texture), then call glUniform1i() and pass the second texture to the shader (and draw). So now my initialise() code is as follows:

//LEFT IMAGE
glActiveTexture(GL_TEXTURE0);
glGenTextures(1, &m_uiTexture_left);                                    
glBindTexture(GL_TEXTURE_2D, m_uiTexture_left);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, pwr2Width, pwr2Height,0, GL_RGB, GL_UNSIGNED_BYTE, xImageL); 
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
GLfloat afVertices[30] = {0.0};
genVertices(afVertices);
glGenBuffers(1, &m_ui32Vbo_leftimage);                                  
m_ui32VertexStride = 5 * sizeof(GLfloat); // 3 floats for the pos, 2 for the UVs
glBindBuffer(GL_ARRAY_BUFFER, m_ui32Vbo_leftimage);
glBufferData(GL_ARRAY_BUFFER, 6 * m_ui32VertexStride, afVertices, GL_STATIC_DRAW);  
glBindBuffer(GL_ARRAY_BUFFER, 0);

//RIGHT IMAGE
glActiveTexture(GL_TEXTURE1);
glGenTextures(1, &m_uiTexture_right);                                   
glBindTexture(GL_TEXTURE_2D, m_uiTexture_right);   
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, pwr2Width, pwr2Height,0, GL_RGB, GL_UNSIGNED_BYTE, xImageR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glGenBuffers(1, &m_ui32Vbo_rightimage);                     
m_ui32VertexStride = 5 * sizeof(GLfloat); // 3 floats for the pos, 2 for the UVs
glBindBuffer(GL_ARRAY_BUFFER, m_ui32Vbo_rightimage);
glBufferData(GL_ARRAY_BUFFER, 6 * m_ui32VertexStride, afVertices, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);

And my render() code goes like:

//&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&  LEFT IMAGE &&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
glEnable(GL_STENCIL_TEST);
glStencilFunc(GL_NOTEQUAL, 1, 1); //draw on uneven lines only
glUniform1i(glGetUniformLocation(m_uiProgramObject, "sampler2d"), 0); //pass texture unit 0 to shader
glBindBuffer(GL_ARRAY_BUFFER, m_ui32Vbo_leftimage);     // unbound this near the end of initView, so need to re-bind it
glEnableVertexAttribArray(VERTEX_ARRAY);
glVertexAttribPointer(VERTEX_ARRAY, 3, GL_FLOAT, GL_FALSE, m_ui32VertexStride, 0);
glEnableVertexAttribArray(TEXCOORD_ARRAY);
glVertexAttribPointer(TEXCOORD_ARRAY, 2, GL_FLOAT, GL_FALSE, m_ui32VertexStride, (void*) (3 * sizeof(GLfloat)));
glDrawArrays(GL_TRIANGLES, 0, 6);
glBindBuffer(GL_ARRAY_BUFFER, 0);
//&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&  RIGHT IMAGE  &&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
glEnable(GL_STENCIL_TEST);
glStencilFunc(GL_EQUAL, 1, 1);  //draw on even lines only
glUniform1i(glGetUniformLocation(m_uiProgramObject, "sampler2d"), 1);
glBindBuffer(GL_ARRAY_BUFFER, m_ui32Vbo_rightimage);
glEnableVertexAttribArray(VERTEX_ARRAY);
glVertexAttribPointer(VERTEX_ARRAY, 3, GL_FLOAT, GL_FALSE, m_ui32VertexStride, 0);
glEnableVertexAttribArray(TEXCOORD_ARRAY);
glVertexAttribPointer(TEXCOORD_ARRAY, 2, GL_FLOAT, GL_FALSE, m_ui32VertexStride, (void*) (3 * sizeof(GLfloat)));
glDrawArrays(GL_TRIANGLES, 0, 6);
glBindBuffer(GL_ARRAY_BUFFER, 0);

Hope this helps someone someday! :)

2 Textures, 1 Shader - OpenGL ES 2.0

2 Answers