c++ - 来自 FBO 的延迟着色器纹理显示为黑色

Question

我正在尝试使用延迟着色来实现 SSAO，但在延迟片段着色器中访问我的纹理时遇到问题。代码使用 C++/Qt5 并使用 Coin3D 生成 UI 的其余部分(但这在这里并不重要)。

延迟 channel 的片段着色器是:

#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);
}

运行延迟传递的代码是

_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();
}

我知道纹理已在几何缓冲区创建中得到正确处理，因为我可以将它们转储到文件中并获得预期结果。

延期通行证不起作用。着色器编译正确，我在屏幕上得到以下结果:

我代码的最后一部分 (DeferredPassBegin/Debug) 是将 FBO 绘制到屏幕上(如屏幕截图所示)作为 GBuffer 正确的证明。

目前的结果似乎意味着纹理没有正确绑定(bind)到它们各自的制服，但我知道内容是有效的，因为我将纹理转储到文件并得到与上面所示相同的结果。

我在 GBuffer 中的绑定(bind)函数是:

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);
}

最后，纹理是 512/512，我在我的 GBuffer 中创建了它们:

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);

在这个阶段我该如何进一步调试？我知道纹理数据是有效的，但我似乎无法将其正确绑定(bind)到着色器(但我有其他着色器使用从文件加载的纹理并且工作正常)。

--- 编辑 1 ---

根据要求，DeferredPassBegin/Debug 的代码(主要来自 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

啊!!!

所以我预计纹理参数不是强制性的，但当我查看一些代码时，我只是尝试指定我的纹理参数。生成 FBO 纹理时，我现在使用

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);
}

通过此更改，我得到了预期的结果(片段着色器中只有 c，如果我切换到可视化法线/位置，则得到类似的正确结果)。

结论:必须指定延迟着色才能工作的纹理参数(至少在我的应用程序/机器的图形设置中)。