FBO中的延迟着色器纹理显示为黑色

Question

I am trying to use deferred shading to implement SSAO and I have problems to access my textures in the deferred fragment shader. The code is in C++/Qt5 and makes use of Coin3D to generate the rest of the UI (but this shouldn't really matter here).

The fragment shader of the deferred pass is:

#version 150 compatibility 

uniform sampler2D color;
uniform sampler2D position;
uniform sampler2D normal;

uniform vec3 dim;
uniform vec3 camPos;
uniform vec3 camDir;

void main()
{
    // screen position
    vec2 t = gl_TexCoord[0].st;

    // the color
    vec4 c = texture2D(color, t);

    gl_FragColor = c + vec4(1.0, t.x, t.y, 1.0);
}

The code for running the deferred pass is

_geometryBuffer.Unbind();

// push state
{
    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();
    glLoadIdentity();

    glMatrixMode(GL_PROJECTION);
    glPushMatrix();
    glLoadIdentity();

    glPushAttrib(GL_DEPTH_BUFFER_BIT | 
                 GL_COLOR_BUFFER_BIT |
                 GL_LIGHTING_BIT | 
                 GL_SCISSOR_BIT | 
                 GL_POLYGON_BIT |
                 GL_CURRENT_BIT);
    glDisable(GL_DEPTH_TEST);
    glDisable(GL_ALPHA_TEST);
    glDisable(GL_LIGHTING);
    glDisable(GL_COLOR_MATERIAL);
    glDisable(GL_SCISSOR_TEST);
    glDisable(GL_CULL_FACE);
}

// bind shader
// /!\ IMPORTANT to do before specifying locations
_deferredShader->bind();

_CheckGLErrors("deferred");

// specify positions
_deferredShader->setUniformValue("camPos", ...);
_deferredShader->setUniformValue("camDir", ...);
_geometryBuffer.Bind(GBuffer::TEXTURE_TYPE_NORMAL, 2);
_deferredShader->setUniformValue("normal", GLint(2));
_geometryBuffer.Bind(GBuffer::TEXTURE_TYPE_POSITION, 1);
_deferredShader->setUniformValue("position",  GLint(1));
_geometryBuffer.Bind(GBuffer::TEXTURE_TYPE_DIFFUSE, 0);
_deferredShader->setUniformValue("color",  GLint(0));

_CheckGLErrors("bind");

// draw screen quad
{
    glBegin(GL_QUADS);
    glTexCoord2f(0, 0);
    glColor3f(0, 0, 0);
    glVertex2f(-1, -1);

    glTexCoord2f(1, 0);
    glColor3f(0, 0, 0);
    glVertex2f( 1, -1);

    glTexCoord2f(1, 1);
    glColor3f(0, 0, 0);
    glVertex2f( 1,  1);

    glTexCoord2f(0, 1);
    glColor3f(0, 0, 0);
    glVertex2f(-1,  1);
    glEnd();
}

_deferredShader->release();

// for debug
_geometryBuffer.Unbind(2);
_geometryBuffer.Unbind(1);
_geometryBuffer.Unbind(0);
_geometryBuffer.DeferredPassBegin();
_geometryBuffer.DeferredPassDebug();

// pop state
{
    glPopAttrib();

    glMatrixMode(GL_PROJECTION);
    glPopMatrix();

    glMatrixMode(GL_MODELVIEW);
    glPopMatrix();
}

I know that the textures have been correctly processed in the geometry buffer creation because I can dump them into files and get the expected result.

The deferred pass doesn't work. The shader compiled correctly and I get the following result on screen:

And the last part of my code (DeferredPassBegin/Debug) is to draw the FBO to the screen (as shown in screenshot) as a proof that the GBuffer is correct.

The current result seems to mean that the textures are not correctly bound to their respective uniform, but I know that the content is valid as I dumped the textures to files and got the same results as shown above.

My binding functions in GBuffer are:

void GBuffer::Unbind()
{
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
    glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
    glBindFramebuffer(GL_READ_FRAMEBUFFER, 0);
}

void GBuffer::Bind(TextureType type, uint32_t idx)
{
    glActiveTexture(GL_TEXTURE0 + idx);
    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, _textures[static_cast<uint32_t>(type)]);
}

void GBuffer::Unbind(uint32_t idx)
{
    glActiveTexture(GL_TEXTURE0 + idx);
    glDisable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, 0);
}

Finally, the textures are 512/512, and I created them in my GBuffer with:

WindowWidth = WindowHeight = 512;
// Create the FBO
glGenFramebuffers(1, &_fbo);
glBindFramebuffer(GL_FRAMEBUFFER, _fbo);

const uint32_t NUM = static_cast<uint32_t>(NUM_TEXTURES);

// Create the gbuffer textures
glGenTextures(NUM, _textures);
glGenTextures(1, &_depthTexture);

for (unsigned int i = 0 ; i < NUM; i++) {
   glBindTexture(GL_TEXTURE_2D, _textures[i]);
   glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, WindowWidth, WindowHeight, 0, GL_RGBA, GL_FLOAT, NULL);
   glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + i + _firstIndex, GL_TEXTURE_2D, _textures[i], 0);
}

// depth
glBindTexture(GL_TEXTURE_2D, _depthTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT32F, WindowWidth, WindowHeight, 0, GL_DEPTH_COMPONENT, GL_FLOAT, NULL);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, _depthTexture, 0);

GLenum buffers[NUM];
for(uint32_t i = 0; i < NUM; ++i){
    buffers[i] = GLenum(GL_COLOR_ATTACHMENT0 + i + _firstIndex);
}
glDrawBuffers(NUM, buffers);

GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
if (status != GL_FRAMEBUFFER_COMPLETE) {
    printf("FB error, status: 0x%x\n", status);
    return _valid = false;
}

// unbind textures
glBindTexture(GL_TEXTURE_2D, 0);

// restore default FBO
glBindFramebuffer(GL_FRAMEBUFFER, 0);

How can I debug farther at this stage? I know that the texture data is valid, but I can't seem to bind it to the shader correctly (but I have other shaders that use textures loaded from files and which work fine).

--- Edit 1 ---

As asked, the code for DeferredPassBegin/Debug (mostly coming from this tutorial )

void GBuffer::DeferredPassBegin() {
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
    glBindFramebuffer(GL_READ_FRAMEBUFFER, _fbo); 
}

void GBuffer::DeferredPassDebug() {
    GLsizei HalfWidth = GLsizei(_texWidth / 2.0f);
    GLsizei HalfHeight = GLsizei(_texHeight / 2.0f);

    SetReadBuffer(TEXTURE_TYPE_POSITION);
    glBlitFramebuffer(0, 0, _texWidth, _texHeight,
                    0, 0, HalfWidth, HalfHeight, GL_COLOR_BUFFER_BIT, GL_LINEAR);

    SetReadBuffer(TEXTURE_TYPE_DIFFUSE);
    glBlitFramebuffer(0, 0, _texWidth, _texHeight,
                    0, HalfHeight, HalfWidth, _texHeight, GL_COLOR_BUFFER_BIT, GL_LINEAR);

    SetReadBuffer(TEXTURE_TYPE_NORMAL);
    glBlitFramebuffer(0, 0, _texWidth, _texHeight,
                    HalfWidth, HalfHeight, _texWidth, _texHeight, GL_COLOR_BUFFER_BIT, GL_LINEAR); 
 }

Answer 1

Arghk!!!

So I expected that texture parameters were not mandatory, but as I looked at some code, I just tried to specify my texture parameters. When generating the FBO textures, I use now

for (unsigned int i = 0 ; i < NUM; i++) {
    glBindTexture(GL_TEXTURE_2D, _textures[i]);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, WindowWidth, WindowHeight, 0, GL_RGBA, GL_FLOAT, NULL);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + i + _firstIndex, GL_TEXTURE_2D, _textures[i], 0);
}

And with this change, I get the expected result (with only c in the fragment shader, and similar correct results if I switch to visualizing the normal / position).

Conclusion : one must specify the texture parameters for deferred shading to work (at least with the graphics setup of my application / machine).