OpenGL: Render to FBO using multiple textures

Question

I'm experimenting with a renderer. What I want is to write a color buffer and a normal buffer to two separate textures. I got that part figured out.

However, the color buffer is supposed to be a combination of two textures. This should do the trick:

glActiveTexture(GL_TEXTURE0_ARB);
glEnable(GL_TEXTURE_2D);
g_Tex->Bind();

glActiveTexture(GL_TEXTURE1_ARB);
glEnable(GL_TEXTURE_2D);
g_TexNormal->Bind();

    g_Shader->Enable();
        RenderScene();
    g_Shader->Disable();

glActiveTexture(GL_TEXTURE1_ARB);
glDisable(GL_TEXTURE_2D);

glActiveTexture(GL_TEXTURE0_ARB);
glDisable(GL_TEXTURE_2D);

And this is the fragment shader: (GLSL)

uniform sampler2D tex_diffuse;
uniform sampler2D tex_normal;

void main()
{
    gl_FragColor = texture2D(tex_diffuse, gl_TexCoord[0].st);
    //gl_FragColor = texture2D(tex_normal, gl_TexCoord[0].st);
}

However, the second texture is the same as the first! Whichever texture is attached to GL_TEXTURE0 is the one used for both samplers.

Initializing the FBO:

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

glGenTextures(1, &g_FBOTexColor);
glBindTexture(GL_TEXTURE_2D, g_FBOTexColor);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, w, h, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
glBindTexture(GL_TEXTURE_2D, 0);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, g_FBOTexColor, 0);

glGenTextures(1, &g_FBOTexNormal);
glBindTexture(GL_TEXTURE_2D, g_FBOTexNormal);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, w, h, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
glBindTexture(GL_TEXTURE_2D, 0);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT1_EXT, GL_TEXTURE_2D, g_FBOTexNormal, 0);

glGenTextures(1, &g_FBOTexDepth);
glBindTexture(GL_TEXTURE_2D, g_FBOTexDepth);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT24, w, h, 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_BYTE, NULL);
glBindTexture(GL_TEXTURE_2D, 0);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_TEXTURE_2D, g_FBOTexDepth, 0);

glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);

Complete render section:

glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, g_FBOColor);
glPushAttrib(GL_VIEWPORT_BIT | GL_COLOR_BUFFER_BIT);

glViewport(
    0, 0,
    Window::GetSingleton()->GetWidth(), Window::GetSingleton()->GetHeight()
);

GLenum buffers[] = { GL_COLOR_ATTACHMENT0_EXT, GL_COLOR_ATTACHMENT1_EXT };
glDrawBuffers(2, buffers);
//glReadBuffer(GL_COLOR_ATTACHMENT0_EXT | GL_COLOR_ATTACHMENT1_EXT);

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glActiveTexture(GL_TEXTURE0_ARB);
glEnable(GL_TEXTURE_2D);
g_Tex->Bind();

glActiveTexture(GL_TEXTURE1_ARB);
glEnable(GL_TEXTURE_2D);
g_TexNormal->Bind();

    g_Shader->Enable();
        RenderScene();
    g_Shader->Disable();

glActiveTexture(GL_TEXTURE1_ARB);
glDisable(GL_TEXTURE_2D);

glActiveTexture(GL_TEXTURE0_ARB);
glDisable(GL_TEXTURE_2D);

glPopAttrib();
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);

Thanks in advance.

Note that you shouldn't call glActiveTexture or glEnable(GL_TEXTURE_2D) when binding them to be rendered to. You should only use those when you're actually rendering geometry that should display those textures (ie. the result of the render-to-texture). — rdb

knight666 knight666 · Accepted Answer · 2010-10-11T08:41:50

Well I figured it out. :)

The reason my textures didn't work was because I didn't set up the uniform locations. Fixed code:

g_Shader->Enable();

    glActiveTexture(GL_TEXTURE0_ARB);
    glEnable(GL_TEXTURE_2D);
    g_Tex->Bind();
    glUniform1i(glGetUniformLocation(g_Shader->GetProgram(), "tex_diffuse"), 0);

    glActiveTexture(GL_TEXTURE1_ARB);
    glEnable(GL_TEXTURE_2D);
    g_TexNormal->Bind();
    glUniform1i(glGetUniformLocation(g_Shader->GetProgram(), "tex_normal"), 1);

        RenderScene();

    glActiveTexture(GL_TEXTURE1_ARB);
    glDisable(GL_TEXTURE_2D);

    glActiveTexture(GL_TEXTURE0_ARB);
    glDisable(GL_TEXTURE_2D);

g_Shader->Disable();

OpenGL: Render to FBO using multiple textures

1 Answers