OpenGL Framebuffer - 渲染到纹理

Question

我制作了一个应用程序，在它上面渲染天空盒和粒子。我想添加一些效果，我需要使用帧缓冲区来渲染天空盒、粒子颜色、深度和位置以分离纹理。然后我想使用简单的着色器来使用这些纹理中的值并以适当的方式混合它们。我为纹理、帧缓冲区和屏幕四边形（要渲染的简单矩形）编写了辅助类，但不幸的是 - 当我尝试使用它时，什么都没有渲染。

当绑定帧缓冲被注释掉时，我的场景是这样的：

修改着色器显示深度和位置值计算正确。因此问题在于纹理和帧缓冲区的使用方式。一些代码的时间：

Framebuffer 辅助类（仅重要方法）：

void Framebuffer::init(){
    // unbind all textures from openGL
    glBindTexture(GL_TEXTURE_2D, 0);
    glGenFramebuffers(1, &framebuffer);
}

void Framebuffer::bind(){
    glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
}

void Framebuffer::unbind(){
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
}

void Framebuffer::attachTexture(GLuint texture, GLenum attachmentType){
    glBindTexture(GL_TEXTURE_2D, texture);    
    glFramebufferTexture(GL_FRAMEBUFFER, attachmentType, texture, 0);
}

void Framebuffer::drawBuffers(GLsizei n, const GLenum *buffers){
    glDrawBuffers(n, buffers);
}

纹理辅助类：

void Texture::init(GLuint windowWidth, GLuint windowHeight, GLint internalFormat, GLenum format, GLenum type){
    glActiveTexture(GL_TEXTURE0);
    glGenTextures(1, &texture);

    glBindTexture(GL_TEXTURE_2D, texture);  

    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, internalFormat , windowWidth, windowHeight, 0, format, type, 0);

    glBindTexture(GL_TEXTURE_2D, 0);
}

void Texture::bind(){
    glBindTexture(GL_TEXTURE_2D, texture);  
}

void Texture::unbind(){
    glBindTexture(GL_TEXTURE_2D, 0);    
}

GLuint Texture::getId(){
    return texture; 
}

ScreenQuad 类：

void ScreenQuad::init(void){
    vao.createVAO();
    vao.bindVAO();

    vbo.createVBO();
    vbo.addData(vertices, 8*sizeof(GLfloat));

    vbo.bindVBO(GL_ARRAY_BUFFER);
    vbo.uploadDataToGPU(GL_STATIC_DRAW);
    glVertexAttribPointer((GLuint)3, 2, GL_FLOAT, GL_FALSE, 0, NULL);

    loadShaders("shaders/basicPostShader.vp", "shaders/basicPostShader.fp");
}

void ScreenQuad::loadShaders(string vsPath, string fsPath){
    shaderProgram.createProgram();
    shaderProgram.loadVertexShader(vsPath);
    shaderProgram.loadFragmentShader(fsPath);

    glBindAttribLocation(shaderProgram.getProgramID(), 3, "v_coord");

    shaderProgram.linkProgram();
}

void ScreenQuad::draw(GLuint depthTexture, GLuint colorTexture, GLuint positionTexture, GLuint backgroundTexture){
    shaderProgram.bindProgram();
    glEnable(GL_TEXTURE_2D);

    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, depthTexture);
    shaderProgram.setUniform("u_depthtex", 0);
    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, colorTexture);
    shaderProgram.setUniform("u_colortex", 1);
    glActiveTexture(GL_TEXTURE2);
    glBindTexture(GL_TEXTURE_2D, positionTexture);
    shaderProgram.setUniform("u_positiontex", 2);
    glActiveTexture(GL_TEXTURE3);
    glBindTexture(GL_TEXTURE_2D, backgroundTexture);
    shaderProgram.setUniform("u_backgroundtex", 3);

    glEnableVertexAttribArray(3);
    vbo.bindVBO();

    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

    vbo.unbindVBO();
    glDisableVertexAttribArray(3);

    shaderProgram.unbindProgram();
}

以及初始化和渲染场景的方法：

void OpenGLContext::setupScene(void) {
    glClearColor(0.4f, 0.6f, 0.9f, 1.0f);

    //FRAMEBUFFERS:

    skyboxFramebuffer.init();
    skyboxTexture.init(windowWidth, windowHeight, GL_RGBA32F, GL_RGBA, GL_FLOAT);
    skyboxFramebuffer.bind();
    skyboxFramebuffer.attachTexture(skyboxTexture.getId(), GL_COLOR_ATTACHMENT0);
    const GLenum skyboxDrawBuffers[1] = { GL_COLOR_ATTACHMENT0};
    skyboxFramebuffer.drawBuffers(1, skyboxDrawBuffers);
    skyboxFramebuffer.validate();
    skyboxFramebuffer.unbind();

    mainFramebuffer.init();
    mainColorTexture.init(windowWidth, windowHeight, GL_RGBA32F, GL_RGBA, GL_FLOAT);
    mainPositionTexture.init(windowWidth, windowHeight, GL_RGBA32F, GL_RGBA, GL_FLOAT);
    mainDepthTexture.init(windowWidth, windowHeight, GL_DEPTH_COMPONENT, GL_DEPTH_COMPONENT, GL_FLOAT);
    mainFramebuffer.bind();
    mainFramebuffer.attachTexture(mainColorTexture.getId(), GL_COLOR_ATTACHMENT0);
    mainFramebuffer.attachTexture(mainPositionTexture.getId(), GL_COLOR_ATTACHMENT1);
    mainFramebuffer.attachTexture(mainDepthTexture.getId(), GL_DEPTH_ATTACHMENT);
    const GLenum mainDrawBuffers[2] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1};
    mainFramebuffer.drawBuffers(2, mainDrawBuffers);
    mainFramebuffer.validate();
    mainFramebuffer.unbind();

    //SKYBOX:

    skybox->init("resources/skybox/default/",
        "pos_x.tga",
        "neg_x.tga",
        "pos_y.tga",
        "neg_y.tga",
        "pos_z.tga",
        "neg_z.tga");

    //PARTICLES:

    particles->init(scene);

    //SCREENQUAD:

    screenQuad.init();
}

void OpenGLContext::renderScene() {
    glfwGetFramebufferSize(window, &windowWidth, &windowHeight);

    glViewport(0, 0, windowWidth, windowHeight);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

    fpsCounter->calcFPS(1.0, windowName);
    if(mode==INPUT_ENABLED_MODE){
        updateInputs();
    }

    projectionMatrix = controls->getProjectionMatrix();
    viewMatrix = controls->getViewMatrix();
    modelMatrix = glm::mat4(1.0f);

    glm::mat4 mvpMatrix = projectionMatrix*viewMatrix*modelMatrix;

    //SKYBOX:
    skyboxFramebuffer.bind();
    skybox->render(mvpMatrix);
    skyboxFramebuffer.unbind();
    //PARTICLES:

    if(scene->tryLockScene()){
        if(scene->isSceneUpdated()){
            particles->updateParticlesPosition(scene);
            scene->setSceneUpdated(false);
        }
        scene->unlockScene();
    }
    mainFramebuffer.bind();
    particles->draw(modelMatrix, viewMatrix, projectionMatrix);
    mainFramebuffer.unbind();
    //SCREENQUAD:

    screenQuad.draw(mainDepthTexture.getId(), mainColorTexture.getId(), mainPositionTexture.getId(), skyboxTexture.getId());

    glfwSwapBuffers(window);
    glfwPollEvents();
}

加上 screenQuad 着色器： 顶点：

#version 430

layout (location = 3) in vec2 v_coord;
layout (binding = 0) uniform sampler2D u_depthtex;
layout (binding = 1) uniform sampler2D u_colortex;
layout (binding = 2) uniform sampler2D u_positiontex;
layout (binding = 3) uniform sampler2D u_backgroundtex;
out vec2 fs_texcoord;

void main(void) {
  gl_Position = vec4(v_coord, 0.0, 1.0);
  fs_texcoord = (v_coord + 1.0) / 2.0;
}

和片段：

#version 430

layout (binding = 0) uniform sampler2D u_depthtex;
layout (binding = 1) uniform sampler2D u_colortex;
layout (binding = 2) uniform sampler2D u_positiontex;
layout (binding = 3) uniform sampler2D u_backgroundtex;
layout (location = 0) out vec4 out_Color;
in vec2 fs_texcoord;

void main(void) {

  float exp_depth = texture(u_depthtex,fs_texcoord).r;

  if(exp_depth>0.99f){
    out_Color = vec4(texture(u_backgroundtex,fs_texcoord).xyz,1.0f);
    return;
  }

  out_Color = vec4(texture(u_colortex,fs_texcoord).xyz, 1.0f);
}

着色器辅助类、vao 和 vbo 辅助类肯定没问题。日志中没有错误发生。

更新： 粒子顶点着色器：

#version 430

uniform mat4x4 modelViewMatrix;
uniform mat4x4 projectionMatrix;

uniform float pointRadius;  // point size in world space
uniform float pointScale;   // scale to calculate size in pixels

layout (location = 0) in vec3 in_Position;
layout (location = 1) in vec4 in_Color;

out vec3 fs_PosEye;
out vec4 fs_Position;
out vec4 fs_Color;

void main(void) {

    vec3 posEye = (modelViewMatrix *  vec4(in_Position.xyz, 1.0f)).xyz;
    float dist = length(posEye);
    gl_PointSize = pointRadius * (pointScale/dist);

    fs_PosEye = posEye;
    fs_Position = modelViewMatrix *  vec4(in_Position.xyz, 1.0f);
    fs_Color = in_Color;
    gl_Position = projectionMatrix * modelViewMatrix  *  vec4(in_Position.xyz, 1.0f);

}

片段着色器：

#version 430

uniform mat4x4 modelViewMatrix;
uniform mat4x4 projectionMatrix;

uniform float pointRadius;  // point size in world space
uniform float pointScale;   // scale to calculate size in pixels

in vec4 fs_Position;
in vec3 fs_PosEye;
in vec4 fs_Color;

layout (location = 0) out vec4 out_Color;
layout (location = 1) out vec4 out_Position;

void main(void)
{
    // calculate normal from texture coordinates
    vec3 normal;
    normal.xy = gl_PointCoord.xy*vec2(2.0, -2.0) + vec2(-1.0, 1.0);
    float r = dot(normal.xy, normal.xy);

    if(r>1.0) 
        discard;

    normal.z = sqrt(1.0-r);

    //calculate depth

    vec4 pixelPos = vec4(fs_PosEye + normalize(normal)*pointRadius,1.0f);
    vec4 clipSpacePos = projectionMatrix * pixelPos;
    gl_FragDepth = (clipSpacePos.z / clipSpacePos.w);

    out_Color = fs_Color;
    out_Position = pixelPos;
}

和 Particles.draw() 方法：

void CParticles::draw(glm::mat4 modelMatrix, glm::mat4 viewMatrix, glm::mat4 projectionMatrix){
    shaderProgram.bindProgram();

    glm::mat4 modelViewMatrix = viewMatrix*modelMatrix;

    shaderProgram.setUniform("projectionMatrix", &projectionMatrix);
    shaderProgram.setUniform("modelViewMatrix", &modelViewMatrix);

    shaderProgram.setUniform("pointRadius", &pointRadius);
    shaderProgram.setUniform("pointScale", &pointScale);

    glPointParameteri(GL_POINT_SPRITE_COORD_ORIGIN, GL_LOWER_LEFT);
    glEnable(GL_POINT_SPRITE);
    glEnable(GL_PROGRAM_POINT_SIZE);

    glDepthMask(GL_TRUE);
    glEnable(GL_DEPTH_TEST);

    glEnableVertexAttribArray(0);
    glEnableVertexAttribArray(1);

    glDrawArrays(GL_POINTS, 0, n);

    glDisableVertexAttribArray(0);
    glDisableVertexAttribArray(1);

    glDisable(GL_PROGRAM_POINT_SIZE);
    glDisable(GL_POINT_SPRITE);

    shaderProgram.unbindProgram();
}

更新2：

问题是当我尝试在 screenQuad 着色器中从它们中采样数据时，由粒子着色器填充的纹理是空的。每个深度、位置和颜色纹理采样器都返回零。我使用与天空盒相同的类和相同的方法，但天空盒纹理效果很好。

更新3： 随机代码更改告诉我，如果我将深度纹理附加到帧缓冲区的注释行，粒子颜色最终会传递给纹理，我可以在屏幕四边形上看到它（但没有任何深度测试。红色粒子（最后绘制）总是打开前）。

我猜想将粒子着色器与深度纹理连接起来有问题。但我仍然找不到确切的错误。我希望我的建议会有所帮助。

Answer 1

我没有研究完整的代码，但是马上跳出来一个问题：

glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, colorTexture);
shaderProgram.setUniform("u_colortex", colorTexture);

纹理采样器的制服值不是纹理 ID（也称为名称）。它是纹理绑定到的纹理单元。所以在这种情况下，由于您为此纹理使用纹理单元 1，它应该是：

shaderProgram.setUniform("u_colortex", 1);

Answer 2

问题是当我调用glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT); 时glDepthMask() 被禁用。

需要启用它才能使glClear(GL_DEPTH_BUFFER_BIT)生效。

另外，我还需要以适当的方式添加清理帧缓冲区。