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opengl使用帧缓冲区及模板缓存记录

程序员文章站 2023-12-24 21:27:39
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opengl使用帧缓冲区及模板缓存记录

这篇文章用于记录学习帧缓存区过程中的一些知识点，由于大部分文章所涉及的知识点都是相似的，所以只能自己在摸索的过程中记录一二，目前只是初学，可能还有很多地方理解出现偏差，请各位大佬批评指正。

  1. 创建帧缓存区

    glGenBuffers(1,&fbo);

    创建帧缓存区的步骤比较简单，只需在创建好后绑定到合适的绑定点上。

    接下来需要创建深度、模板和颜色缓冲区，用于添加到帧缓存区

    glGenRenderbuffers(1,&depthbuffer);//创建深度、模板缓存区（即选择GL_DEPTH24_STENCIL8参数
glBindRenderbuffer(GL_RENDERBUFFER, depthbuffer);
glRenderbufferStorage(GL_RENDERBUFFER,GL_DEPTH24_STENCIL8,800,600);

glGenBuffers(2,colorbuffer);//创建两个颜色缓存区，用于绘制两种图像
glBindRenderbuffer(GL_RENDERBUFFER,colorbuffer[0]);
glRenderbufferStorage(GL_RENDERBUFFER,GL_RGBA8,800,600);
glBindRenderbuffer(GL_RENDERBUFFER,colorbuffer[1]);
glRenderbufferStorage(GL_RENDERBUFFER,GL_RGBA8,800,600);

    在创建完成之后需要将这些缓存区添加到帧缓存区当中。

    glBindFramebuffer(GL_DRAW_FRAMEBUFFER,fbo);//绑定fbo为帧缓冲区
glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER,GL_DEPTH_STENCIL_ATTACHMENT,GL_RENDERBUFFER,depthbuffer);
glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER,GL_COLOR_ATTACHMENT0,GL_RENDERBUFFER,colorbuffer[0]);//绑定在颜色缓冲区0
glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER,GL_COLOR_ATTACHMENT1,GL_RENDERBUFFER,colorbuffer[1]);//绑定在颜色缓冲区1

    这样就完成了帧缓存区的创建

  2. 创建shader

    顶点着色器和普通的没有区别，只能片段着色器会多一个输出，因为有两个颜色缓冲区。片段着色器代码如下：

    #version 130
in vec2 texcoord;
out vec4 vFragColor;
out vec4 oStraightColor;
uniform sampler2D grid;//纹理
uniform int flag;//用于模板缓存的标志位
void main(void)
{
    if(flag==1)
    {
        vFragColor = vec4(vec3(texture(grid, texcoord).r), 1.0);
        oStraightColor = vec4(1.0);
    }
    else
    {
        vFragColor = vec4(0.04, 0.28, 0.26, 1.0);
        oStraightColor = vec4(0.04, 0.28, 0.26, 1.0);
    }
}

    在创建完shader之后还需要将片段着色器的输出vFragColor和oStraightColor与颜色缓冲区进行绑定，即

    glBindFragDataLocation(diffuseLightShader, 0, "vFragColor");//绑定在0号颜色缓冲区
glBindFragDataLocation(diffuseLightShader, 1, "oStraightColor");//绑定在1号颜色缓冲区

    到这里就完成了所有初始化的操作，接下来可以开始绘制。

  3. 渲染主循环

    首先需要设置使用帧缓存区，否则会按照默认直接绘制到屏幕上。

    glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo);
glDrawBuffers(2,fboBuffs);//fboBuffs是GL_COLOR_ATTACHMENT0和GL_COLOR_ATTACHMENT1的数组头指针。

    然后按照正常的绘制操作完成绘制，即

    glUniformMatrix4fv(locMVP,1,GL_FALSE,transformPipeline.GetModelViewProjectionMatrix());
glUniform1i(glGetUniformLocation(diffuseLightShader,"grid"),0);
glUniform1i(glGetUniformLocation(diffuseLightShader,"flag"),1);//flag=1表示绘制原始纹理，而不是纯色
glBindVertexArray(vao); 
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

    到这一步为止屏幕上是没有输出的，因为都绘制到缓冲区fbo上了。

    接下来就是把缓冲区的内容输出到屏幕上，

    glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);//设置输出缓冲区为0,即屏幕
glDrawBuffers(1, windowBuff);
glViewport(0, 0, 800, 600);

glBindFramebuffer(GL_READ_FRAMEBUFFER, fbo);//设置从fbo读取数据用于输出
//上述部分实现了设置从fbo读取图像数据输出到屏幕，接下来将各个颜色缓冲区输出。
glReadBuffer(GL_COLOR_ATTACHMENT0);
glBlitFramebuffer(0, 0, 800, 600,
                  0, 0, 800, 600,
                  GL_COLOR_BUFFER_BIT, GL_NEAREST );


glReadBuffer(GL_COLOR_ATTACHMENT1);
glBlitFramebuffer(0, 0, 800, 600,
                  (int)(800 *(0.8)), (int)(600*(0.8)),
                  800, 600,
                  GL_COLOR_BUFFER_BIT, GL_LINEAR );

    现在就能在屏幕上看见绘制的内容了。

  4. 加入模板测试绘制边框

    我们现在只是使用了之前创建的两个颜色缓冲区，接下来使用模板缓存绘制边框。关于模板测试的用法即原理可以参考StencilTest 。

    在调用glDrawArrays之前需要启用模板测试，并清空缓存区。

    glEnable(GL_STENCIL_TEST);
glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
glEnable(GL_DEPTH_TEST);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

    然后在第一次绘制的之前添加以下代码，将需要绘制的部分模板值设为1

    glStencilFunc(GL_ALWAYS, 1, 0xFF);
glStencilMask(0xFF);

    在第一次绘制完成后，将所绘制的图像放大modelViewMatrix.Scale(1.05f,1.05f,1.05f)

    然后再次设置模板测试，实现只绘制边界

    glStencilFunc(GL_NOTEQUAL, 1, 0xFF);
glStencilMask(0x00);
glDisable(GL_DEPTH_TEST);

    然后调用绘制程序，此时将 flag设为0，只输出纯色，最终实现效果如下：
    opengl使用帧缓冲区及模板缓存记录

  5. 后记

    • 在绘制边框的时候需要使用与第一次绘制相同的着色器，通过flag调节着色器的输出。本来采用单独的一个着色器输出纯色，但是会导致无法输出到两个颜色缓冲区，暂时还没有学习到相关方法。
    • 在使用帧缓存区时，需要输出到两个颜色缓存区，但是将gl的版本设置为3.0以上会出现输出到两个缓存区的结果一样（或者只使用了一个缓冲区），无法实现缩略图的效果。官方文档在3.0版本对FBO进行了更新，但是以现有水平难以理解文档内容。gl版本设置为3.0以下时可以实现上述效果。

  6. 完整代码

    // DiffuseLight.cpp
// OpenGL SuperBible
// Demonstrates simple diffuse lighting
// Program by Richard S. Wright Jr.

#include <GLTools.h>    // OpenGL toolkit
#include <GLMatrixStack.h>
#include <GLFrame.h>
#include <GLFrustum.h>
#include <GLGeometryTransform.h>
#include <StopWatch.h>

#include <math.h>
#ifdef __APPLE__
#include <glut/glut.h>
#else
#define FREEGLUT_STATIC
#include <GL/glut.h>
#include <GL/freeglut_ext.h>
#endif


GLFrame             viewFrame;
GLFrustum           viewFrustum;
GLTriangleBatch     sphereBatch;
GLMatrixStack       modelViewMatrix;
GLMatrixStack       projectionMatrix;
GLGeometryTransform transformPipeline;
GLShaderManager     shaderManager;

GLuint	diffuseLightShader;	// The diffuse light shader
GLint	locMVP;				// The location of the ModelViewProjection matrix uniform
GLuint singlecolorShader;
static GLuint               fbo,texture;
static GLuint               depthbuffer, colorbuffer[2],stencilbuffer;
static const GLenum windowBuff[] = { GL_BACK_LEFT };
static const GLenum fboBuffs[] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1 };
unsigned int vertexBuffer, vao ;

float lastX = 400;
float lastY = 300;
float yaw = 0;
float pitch = 0;
float front[3] = {0,0,-1};
bool first_mouse = true;
// This function does any needed initialization on the rendering
// context.
void SetupRC(void)
{
    // Background
    glClearColor(0.2f, 0.3f, 0.2f, 1.0f );

    glEnable(GL_DEPTH_TEST);
    //glEnable(GL_CULL_FACE);

    viewFrame.MoveForward(4.0f);

    glGenBuffers(1,&fbo);

    glGenRenderbuffers(1,&depthbuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, depthbuffer);
    glRenderbufferStorage(GL_RENDERBUFFER,GL_DEPTH24_STENCIL8,800,600);

    glGenBuffers(2,colorbuffer);
    glBindRenderbuffer(GL_RENDERBUFFER,colorbuffer[0]);
    glRenderbufferStorage(GL_RENDERBUFFER,GL_RGBA8,800,600);
    glBindRenderbuffer(GL_RENDERBUFFER,colorbuffer[1]);
    glRenderbufferStorage(GL_RENDERBUFFER,GL_RGBA8,800,600);

    glBindFramebuffer(GL_DRAW_FRAMEBUFFER,fbo);
    glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER,GL_DEPTH_STENCIL_ATTACHMENT,GL_RENDERBUFFER,depthbuffer);
    glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER,GL_COLOR_ATTACHMENT0,GL_RENDERBUFFER,colorbuffer[0]);
    glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER,GL_COLOR_ATTACHMENT1,GL_RENDERBUFFER,colorbuffer[1]);

    diffuseLightShader = shaderManager.LoadShaderPairWithAttributes("Perspective.vs", "Perspective.fs",
                                                                    2,
                                                                    GLT_ATTRIBUTE_VERTEX, "vVertex",
                                                                    GLT_ATTRIBUTE_TEXTURE0, "vTexCoord");
    glBindFragDataLocation(diffuseLightShader, 0, "vFragColor");
    glBindFragDataLocation(diffuseLightShader, 1, "oStraightColor");


    locMVP = glGetUniformLocation(diffuseLightShader, "mvpMatrix");


    singlecolorShader = shaderManager.LoadShaderPairWithAttributes("Perspective.vs", "Perspective2.fs",
                                                                   2,
                                                                   GLT_ATTRIBUTE_VERTEX, "vVertex",
                                                                   GLT_ATTRIBUTE_TEXTURE0, "vTexCoord");
    // Geometry for a simple quad
    static const GLfloat quad[] =
            {
                    -1.0f, -1.0f, 0.0f,
                    1.0f, -1.0f, 0.0f,
                    1.0f,  1.0f, 0.0f,
                    -1.0f,  1.0f, 0.0f,
            };

    static const GLfloat texcoords[] =
            {
                    0.0f, 0.0f,
                    1.0f, 0.0f,
                    1.0f, 1.0f,
                    0.0f, 1.0f
            };

    // A checkerboard texture
    static const GLubyte texture_data[] =
            {
                    0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255,
                    255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0,
                    0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255,
                    255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0,
                    0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255,
                    255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0,
                    0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255,
                    255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0,
                    0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255,
                    255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0,
                    0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255,
                    255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0,
                    0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255,
                    255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0,
                    0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255,
                    255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0
            };

    // Greate a vertex array object and a vertex buffer for the quad
    // including position and texture coordinates
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);
    glGenBuffers(1, &vertexBuffer);
    glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(quad) + sizeof(texcoords), NULL, GL_STATIC_DRAW);
    glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(quad), quad);
    glBufferSubData(GL_ARRAY_BUFFER, sizeof(quad), sizeof(texcoords), texcoords);
    glVertexAttribPointer(GLT_ATTRIBUTE_VERTEX, 3, GL_FLOAT, GL_FALSE, 0, NULL);
    glVertexAttribPointer(GLT_ATTRIBUTE_TEXTURE0, 2, GL_FLOAT, GL_FALSE, 0, (GLvoid *)sizeof(quad));
    glEnableVertexAttribArray(GLT_ATTRIBUTE_VERTEX);
    glEnableVertexAttribArray(GLT_ATTRIBUTE_TEXTURE0);

    // Create the checkerboard texture
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, 16, 16, 0, GL_RED, GL_UNSIGNED_BYTE, texture_data);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

}

// Cleanup
void ShutdownRC(void)
{

}


// Called to draw scene
void RenderScene(void)
{
    static CStopWatch rotTimer;
    glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo);
    glDrawBuffers(2,fboBuffs);
    glEnable(GL_STENCIL_TEST);
    glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
    glEnable(GL_DEPTH_TEST);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
    glClearColor(0.5f, 0.5f, 0.5f, 1.0f );
    M3DMatrix44f mCamera;
    viewFrame.GetCameraMatrix(mCamera);

    modelViewMatrix.PushMatrix(viewFrame);
    modelViewMatrix.Rotate(rotTimer.GetElapsedSeconds() * 10.0f, 0.0f, 1.0f, 0.0f);

    glUseProgram(diffuseLightShader);

    glStencilFunc(GL_ALWAYS, 1, 0xFF);
    glStencilMask(0xFF);

    glUniformMatrix4fv(locMVP, 1, GL_FALSE, transformPipeline.GetModelViewProjectionMatrix());
    glUniform1i(glGetUniformLocation(diffuseLightShader,"grid"),0);
    glUniform1i(glGetUniformLocation(diffuseLightShader,"flag"),1);
    glBindVertexArray(vao); // seeing as we only have a single VAO there's no need to bind it every time, but we'll do so to keep things a bit more organized
    glDrawArrays(GL_TRIANGLE_FAN, 0, 4);


    modelViewMatrix.Scale(1.05f,1.05f,1.05f);

    glStencilFunc(GL_NOTEQUAL, 1, 0xFF);
    glStencilMask(0x00);
    glDisable(GL_DEPTH_TEST);

    glUniformMatrix4fv(locMVP, 1, GL_FALSE, transformPipeline.GetModelViewProjectionMatrix());
    glUniform1i(glGetUniformLocation(diffuseLightShader,"flag"),0);
    glBindVertexArray(vao); // seeing as we only have a single VAO there's no need to bind it every time, but we'll do so to keep things a bit more organized
    glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

    glStencilMask(0xFF);
    glStencilFunc(GL_ALWAYS, 0, 0xFF);
    glEnable(GL_DEPTH_TEST);

    modelViewMatrix.PopMatrix();

    glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
    glDrawBuffers(1, windowBuff);
    glViewport(0, 0, 800, 600);

    glBindFramebuffer(GL_READ_FRAMEBUFFER, fbo);

    glReadBuffer(GL_COLOR_ATTACHMENT0);
    glBlitFramebuffer(0, 0, 800, 600,
                      0, 0, 800, 600,
                      GL_COLOR_BUFFER_BIT, GL_NEAREST );


    glReadBuffer(GL_COLOR_ATTACHMENT1);
    glBlitFramebuffer(0, 0, 800, 600,
                      (int)(800 *(0.8)), (int)(600*(0.8)),
                      800, 600,
                      GL_COLOR_BUFFER_BIT, GL_LINEAR );

    glutSwapBuffers();
    glutPostRedisplay();
}



void ChangeSize(int w, int h)
{
    // Prevent a divide by zero
    if(h == 0)
        h = 1;

    // Set Viewport to window dimensions
    glViewport(0, 0, w, h);

    viewFrustum.SetPerspective(35.0f, float(w)/float(h), 1.0f, 100.0f);

    projectionMatrix.LoadMatrix(viewFrustum.GetProjectionMatrix());
    transformPipeline.SetMatrixStacks(modelViewMatrix, projectionMatrix);
}
void Keyboard(unsigned char key, int x, int y)
{
    float delta = -0.1f;
    switch (key)
    {
        // Space toggles perspective correction
        case 'w':
            viewFrame.MoveForward(-delta);
            break;
        case 's':
            viewFrame.MoveForward(delta);
            break;
        case 'a':
            viewFrame.MoveRight(-delta);
            break;
        case 'd':
            viewFrame.MoveRight(delta);
            break;
        case 27:
            glutLeaveMainLoop();
            break;
        default:
            break;
    };
}
void MouseFunc(int x,int y)
{
    if (first_mouse)
    {
        first_mouse = false;
        lastX = x;
        lastY = y;
    }
    float xoffset = x - lastX;
    float yoffset = y - lastY;
    lastX = x;
    lastY = y;

    float sensitivity = 0.3f;
    sensitivity = m3dDegToRad(sensitivity);
    xoffset *= sensitivity;
    yoffset *= sensitivity;

    viewFrame.RotateWorld(-xoffset,0.0f,1.0f,0.0f);
    //viewFrame.RotateWorld(-yoffset,1.0f,0.0f,0.0f);
}

void EntryFunc(int state)
{
    if(state == GLUT_LEFT)
    {
        first_mouse = true;
    }
}

///
// Main entry point for GLUT based programs
int main(int argc, char* argv[])
{
    gltSetWorkingDirectory(argv[0]);
    /* 1, 3 */
    glutInitContextVersion(1, 3);

    glutInitContextProfile (GLUT_CORE_PROFILE);
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH | GLUT_STENCIL);
    glutInitWindowSize(800, 600);
    glutCreateWindow("Simple Diffuse Lighting");
    glutReshapeFunc(ChangeSize);
    glutDisplayFunc(RenderScene);
    glutKeyboardFunc(Keyboard);
    glutPassiveMotionFunc(MouseFunc);
    glutEntryFunc(EntryFunc);
    GLenum err = glewInit();
    if (GLEW_OK != err) {
        fprintf(stderr, "GLEW Error: %s\n", glewGetErrorString(err));
        return 1;
    }

    SetupRC();
    glutMainLoop();
    ShutdownRC();
    return 0;
}
相关标签： OpenGL opengl c++

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