OpenGL帧缓冲区-渲染到纹理

Question

我做了一个在上面渲染天空盒和粒子的应用程序。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（渲染简单的矩形）编写了辅助类，但不幸的是——当我尝试使用它时没有任何渲染。

当绑定帧缓冲区被注释掉时，我的场景如下所示：

修改着色器表明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：

帧缓冲区帮助器类（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);
}

纹理助手类：

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();
}

加屏幕四着色器：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);
}

着色器助手类、vao和vbo助手类肯定没问题。日志中不会发生错误。

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;
}

还有粒子。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着色器中从粒子着色器填充的纹理中采样数据时，它们是空的。每个深度、位置和颜色纹理采样器返回零。我使用与skybox相同的类和方法，但skybox纹理效果很好。

更新3：随机代码的变化告诉我，如果我在评论行中将深度纹理附加到帧缓冲区，粒子颜色最终会传递到一个纹理，我可以在屏幕上看到它（但没有任何深度测试。红色粒子（最后绘制）总是在前面）。

我想将粒子着色器与深度纹理连接起来可能有问题。但我还是找不到确切的虫子。我希望我的建议会有帮助。

Answer 1

问题是当我调用glClear（GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER|BIT | GL_STENCIL_BUFFER_BIT | GL_STENCIL_BUFFER|BIT | 。

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。

Answer 2

我还没有研究完整的代码，但一个问题马上就出现了：

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

纹理采样器的统一值不是纹理id（又名）。它是纹理绑定到的纹理单元。因此，在这种情况下，由于您将纹理第一单元用于此纹理，它应该是：

shaderProgram.setUniform("u_colortex", 1);