opengl将画面渲染到屏幕的指定区域和多屏渲染

分别将画面渲染到屏幕的左上，坐下，右上，右下区域   效果图：

多屏渲染效果图：

原理见代码注释

 #include "FullScreenQuad.h"


 void FullScreenQuad::Init()
 {
     glGenBuffers(1, &mVBO);
     glBindBuffer(GL_ARRAY_BUFFER, mVBO);
     glBufferData(GL_ARRAY_BUFFER, sizeof(float) * 20, nullptr, GL_STATIC_DRAW);
     glBindBuffer(GL_ARRAY_BUFFER, 0);
 }

 //绘制一个铺满屏幕的四边形
 void FullScreenQuad::Draw(GLint posLoc, GLint texcoordLoc)
 {
     //draw fullscreen
     float vertices[] = {
         -0.5f,-0.5f,-1.0f,0.0f,0.0f,
         0.5f,-0.5f,-1.0f,1.0f,0.0f,
         0.5f,0.5f,-1.0f,1.0f,1.0f,
         -0.5f,0.5f,-1.0f,0.0f,1.0f
     };
     glBindBuffer(GL_ARRAY_BUFFER, mVBO);//绑定到vbo
     glBufferData(GL_ARRAY_BUFFER, sizeof(float) * 20, vertices, GL_STATIC_DRAW);//顶点数据上传至显卡
     glBindBuffer(GL_ARRAY_BUFFER, 0);

     glBindBuffer(GL_ARRAY_BUFFER, mVBO);
     glEnableVertexAttribArray(posLoc);//启用顶点坐标属性
     //指定顶点数据在VBO中的入口地址
     glVertexAttribPointer(posLoc, 3, GL_FLOAT, GL_FALSE, sizeof(float) * 5, 0);
     glEnableVertexAttribArray(texcoordLoc);//启用顶点纹理坐标属性
     //指定顶点纹理坐标在VBO中的入口地址
     glVertexAttribPointer(texcoordLoc, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 5, (void*)(sizeof(float)*3));
     glDrawArrays(GL_QUADS, 0, 4);
     glBindBuffer(GL_ARRAY_BUFFER, 0);
 }


 //绘制左上角四分之一的矩形
 void FullScreenQuad::DrawToLeftTop(GLint posLoc, GLint texcoordLoc)
 {

     float vertices[] = {
         -0.5f,0.0f,-1.0f,0.0f,0.0f,
         0.0f,0.0f,-1.0f,1.0f,0.0f,
         0.0f,0.5f,-1.0f,1.0f,1.0f,
         -0.5f,0.5f,-1.0f,0.0f,1.0f
     };
     glBindBuffer(GL_ARRAY_BUFFER, mVBO);
     glBufferData(GL_ARRAY_BUFFER, sizeof(float) * 20, vertices, GL_STATIC_DRAW);
     glBindBuffer(GL_ARRAY_BUFFER, 0);

     glBindBuffer(GL_ARRAY_BUFFER, mVBO);
     glEnableVertexAttribArray(posLoc);
     glVertexAttribPointer(posLoc, 3, GL_FLOAT, GL_FALSE, sizeof(float) * 5, 0);

     glEnableVertexAttribArray(texcoordLoc);
     glVertexAttribPointer(texcoordLoc, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 5, (void*)(sizeof(float) * 3));
     glDrawArrays(GL_QUADS, 0, 4);
     glBindBuffer(GL_ARRAY_BUFFER, 0);
 }


 //绘制左下角四分之的矩形
 void FullScreenQuad::DrawToLeftBottom(GLint posLoc, GLint texcoordLoc)
 {

     float vertices[] = {
         -0.5f,-0.5f,-1.0f,0.0f,0.0f,
         0.0f,-0.5f,-1.0f,1.0f,0.0f,
         0.0f,0.0f,-1.0f,1.0f,1.0f,
         -0.5f,0.0f,-1.0f,0.0f,1.0f
     };
     glBindBuffer(GL_ARRAY_BUFFER, mVBO);
     glBufferData(GL_ARRAY_BUFFER, sizeof(float) * 20, vertices, GL_STATIC_DRAW);
     glBindBuffer(GL_ARRAY_BUFFER, 0);

     glBindBuffer(GL_ARRAY_BUFFER, mVBO);
     glEnableVertexAttribArray(posLoc);
     glVertexAttribPointer(posLoc, 3, GL_FLOAT, GL_FALSE, sizeof(float) * 5, 0);
     glEnableVertexAttribArray(texcoordLoc);
     glVertexAttribPointer(texcoordLoc, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 5, (void*)(sizeof(float) * 3));
     glDrawArrays(GL_QUADS, 0, 4);
     glBindBuffer(GL_ARRAY_BUFFER, 0);
 }


 //绘制右上角四分之一的矩形
 void FullScreenQuad::DrawToRightTop(GLint posLoc, GLint texcoordLoc)
 {

     float vertices[] = {
         0.0f,-0.0f,-1.0f,0.0f,0.0f,
         0.5f,-0.0f,-1.0f,1.0f,0.0f,
         0.5f,0.5f,-1.0f,1.0f,1.0f,
         0.0f,0.5f,-1.0f,0.0f,1.0f
     };
     glBindBuffer(GL_ARRAY_BUFFER, mVBO);
     glBufferData(GL_ARRAY_BUFFER, sizeof(float) * 20, vertices, GL_STATIC_DRAW);
     glBindBuffer(GL_ARRAY_BUFFER, 0);

     glBindBuffer(GL_ARRAY_BUFFER, mVBO);
     glEnableVertexAttribArray(posLoc);
     glVertexAttribPointer(posLoc, 3, GL_FLOAT, GL_FALSE, sizeof(float) * 5, 0);
     glEnableVertexAttribArray(texcoordLoc);
     glVertexAttribPointer(texcoordLoc, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 5, (void*)(sizeof(float) * 3));
     glDrawArrays(GL_QUADS, 0, 4);
     glBindBuffer(GL_ARRAY_BUFFER, 0);
 }

 //绘制右下角四分之的矩形
 void FullScreenQuad::DrawToRightBottom(GLint posLoc, GLint texcoordLoc)
 {

     float vertices[] = {
         0.0f,-0.5f,-1.0f,0.0f,0.0f,
         0.5f,-0.5f,-1.0f,1.0f,0.0f,
         0.5f,0.0f,-1.0f,1.0f,1.0f,
         0.0f,0.0f,-1.0f,0.0f,1.0f
     };
     glBindBuffer(GL_ARRAY_BUFFER, mVBO);
     glBufferData(GL_ARRAY_BUFFER, sizeof(float) * 20, vertices, GL_STATIC_DRAW);
     glBindBuffer(GL_ARRAY_BUFFER, 0);

     glBindBuffer(GL_ARRAY_BUFFER, mVBO);
     glEnableVertexAttribArray(posLoc);
     glVertexAttribPointer(posLoc, 3, GL_FLOAT, GL_FALSE, sizeof(float) * 5, 0);
     glEnableVertexAttribArray(texcoordLoc);
     glVertexAttribPointer(texcoordLoc, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 5, (void*)(sizeof(float) * 3));
     glDrawArrays(GL_QUADS, 0, 4);
     glBindBuffer(GL_ARRAY_BUFFER, 0);
 }

渲染入口

渲染步骤

一，使用带光照效果的shader

1,首先创建一个fbo

2,在此fbo中绘制三个带光照效果的立方体(每个立方体都有各自的模型矩阵和法线矩阵)

3,分别设置三个立方体的光源并绘制

二，切换shader，使用绘制四边形的shader

4,分别在屏幕的左上，左下，右上，右下绘制四个四边形

5,将此前绘制在fbo中的内容作为纹理贴在绘制的四个四边形中

 #include
 #include "glew.h"
 #include
 #include
 #include "utils.h"
 #include "GPUProgram.h"
 #include "ObjModel.h"
 #include "FBO.h"
 #include "FullScreenQuad.h"
 #include "Glm/glm.hpp"
 #include "Glm/ext.hpp"
 #pragma comment(lib,"opengl32.lib")
 #pragma comment(lib,"glew32.lib")

 LRESULT CALLBACK GLWindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
 {
     switch (msg)
     {
     case WM_CLOSE:
         PostQuitMessage(0);
         break;
     }
     return DefWindowProc(hwnd,msg,wParam,lParam);
 }


 INT WINAPI WinMain(_In_ HINSTANCE hInstance, _In_opt_ HINSTANCE hPrevInstance, _In_ LPSTR lpCmdLine, _In_ int nShowCmd)
 {
     WNDCLASSEX wndClass;
     wndClass.cbClsExtra = 0;
     wndClass.cbSize = sizeof(WNDCLASSEX);
     wndClass.cbWndExtra = 0;
     wndClass.hbrBackground = NULL;
     wndClass.hCursor = LoadCursor(NULL,IDC_ARROW);
     wndClass.hIcon = NULL;
     wndClass.hIconSm = NULL;
     wndClass.hInstance = hInstance;
     wndClass.lpfnWndProc=GLWindowProc;
     wndClass.lpszClassName = L"OpenGL";
     wndClass.lpszMenuName = NULL;
     wndClass.style = CS_VREDRAW | CS_HREDRAW;
     ATOM atom = RegisterClassEx(&wndClass);

     RECT rect;
     rect.left = 0;
     rect.top = 0;
     rect.right = 800;
     rect.bottom = 600;
     AdjustWindowRect(&rect, WS_OVERLAPPEDWINDOW, FALSE);
     HWND hwnd = CreateWindowEx(NULL, L"OpenGL", L"RenderWindow", WS_OVERLAPPEDWINDOW, 100, 100, rect.right-rect.left, rect.bottom-rect.top, NULL, NULL, hInstance, NULL);
     HDC dc = GetDC(hwnd);
     PIXELFORMATDESCRIPTOR pfd;
     memset(&pfd, 0, sizeof(PIXELFORMATDESCRIPTOR));
     pfd.nVersion = 1;
     pfd.dwFlags = PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_TYPE_RGBA | PFD_DOUBLEBUFFER;
     pfd.iLayerType = PFD_MAIN_PLANE;
     pfd.iPixelType = PFD_TYPE_RGBA;
     pfd.cColorBits = 32;
     pfd.cDepthBits = 24;
     pfd.cStencilBits = 8;

     int pixelFormatID = ChoosePixelFormat(dc, &pfd);

     SetPixelFormat(dc,pixelFormatID,&pfd);

     HGLRC rc = wglCreateContext(dc);
     wglMakeCurrent(dc, rc);
     GetClientRect(hwnd, &rect);
     int viewportWidth = rect.right - rect.left, viewportHeight = rect.bottom - rect.top;
     glewInit();

     GPUProgram fsqProgram;
     fsqProgram.AttachShader(GL_VERTEX_SHADER, "Debug/res/shader/fullscreenquad.vs");
     fsqProgram.AttachShader(GL_FRAGMENT_SHADER, "Debug/res/shader/fullscreenquad.fs");
     fsqProgram.Link();

     fsqProgram.DetectAttribute("pos");
     fsqProgram.DetectAttribute("texcoord");
     fsqProgram.DetectUniform("U_MainTexture");

     GPUProgram gpuProgram;
     gpuProgram.AttachShader(GL_VERTEX_SHADER, "Debug/res/shader/Light.vs");
     gpuProgram.AttachShader(GL_FRAGMENT_SHADER, "Debug/res/shader/Light.fs");
     gpuProgram.Link();

     gpuProgram.DetectAttribute("pos");
     gpuProgram.DetectAttribute("texcoord");
     gpuProgram.DetectAttribute("normal");
     gpuProgram.DetectUniform("M");
     gpuProgram.DetectUniform("V");
     gpuProgram.DetectUniform("P");
     gpuProgram.DetectUniform("NM");
     gpuProgram.DetectUniform("U_AmbientLightColor");
     gpuProgram.DetectUniform("U_AmbientMaterial");
     gpuProgram.DetectUniform("U_DiffuseLightColor");
     gpuProgram.DetectUniform("U_DiffuseMaterial");
     gpuProgram.DetectUniform("U_SpecularLightColor");
     gpuProgram.DetectUniform("U_SpecularMaterial");
     gpuProgram.DetectUniform("U_LightPos");
     gpuProgram.DetectUniform("U_EyePos");
     gpuProgram.DetectUniform("U_LightDirection");
     gpuProgram.DetectUniform("U_Cutoff");
     gpuProgram.DetectUniform("U_DiffuseIntensity");
     //init 3d model
     ObjModel cube;
     cube.Init("Debug/res/model/Cube.obj");

     //摄像机矩阵的单位矩阵
     float identity[] = {
         1.0f,0,0,0,
         0,1.0f,0,0,
         0,0,1.0f,0,
         0,0,0,1.0f
     };
     float ambientLightColor[] = { 0.4f,0.4f,0.4f,1.0f };//环境光颜色
     float ambientMaterial[] = { 0.2f,0.2f,0.2f,1.0f };//环境光材质
     float diffuseLightColor[] = { 1.0f,1.0f,1.0f,1.0f };//漫反射光颜色
     float diffuseMaterial[] = { 0.6f,0.6f,0.6f,1.0f };//漫反射光材质
     float diffuseIntensity = 1.0f;//漫反射光强度
     float specularLightColor[] = { 1.0f,1.0f,1.0f,1.0f };//环境光颜色
     float specularMaterial[] = { 1.0f,1.0f,1.0f,1.0f };//环境光材质
     float lightPos[] = { 0.0f,1.5f,0.0f,0.0f };//光源位置
     float spotLightDirection[] = { 0.0f,-1.0f,0.0f,128.0f };//聚光灯中心线向量
     float spotLightCutoff = 0.0f;// 聚光灯中心线向量和入射光线最大夹角
     float eyePos[] = { 0.0f,0.0f,0.0f };//眼睛的位置

     //模型矩阵
     glm::mat4 model1 = glm::translate<float>(-2.0f, 0.0f, -6.0f)*glm::rotate(-30.0f,1.0f,1.0f,1.0f);
     glm::mat4 model2 = glm::translate<float>(0.0f, 0.0f, -6.0f)*glm::rotate(-30.0f,1.0f,1.0f,1.0f);
     glm::mat4 model3 = glm::translate<float>(2.0f, 0.0f, -6.0f)*glm::rotate(-30.0f,1.0f,1.0f,1.0f);
     //投影矩阵
     glm::mat4 projectionMatrix = glm::perspective(50.0f, (float)viewportWidth / (float)viewportHeight, 0.1f, 1000.0f);

     //将法线转换到世界空间的变换矩阵
     glm::mat4 normalMatrix1 = glm::inverseTranspose(model1);
     glm::mat4 normalMatrix2 = glm::inverseTranspose(model2);
     glm::mat4 normalMatrix3 = glm::inverseTranspose(model3);


     FullScreenQuad fsq;
     fsq.Init();
     FBO fbo;
     fbo.AttachColorBuffer("color", GL_COLOR_ATTACHMENT0, GL_RGBA, viewportWidth, viewportHeight);
     fbo.AttachDepthBuffer("depth", viewportWidth, viewportHeight);
     fbo.Finish();

     //glClearColor(41.0f/255.0f,  71.0f/255.0f, 121.0f / 255.0f, 1.0f);
     ShowWindow(hwnd, SW_SHOW);
     UpdateWindow(hwnd);

     bool isFullScreen = true;
     MSG msg;
     while (true)
     {
         if (PeekMessage(&msg,NULL,NULL,NULL,PM_REMOVE))
         {
             if (msg.message==WM_QUIT)
             {
                 break;
             }
             TranslateMessage(&msg);
             DispatchMessage(&msg);
         }
         //绑定fbo----将绘制的场景绑定到FBO
         fbo.Bind();

         glClearColor(0.0f,0.0f,0.0f,1.0f);
         //这步很重要
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
         glEnable(GL_DEPTH_TEST);

         glUseProgram(gpuProgram.mProgram);
         //设置shader中变量的值
         glUniformMatrix4fv(gpuProgram.GetLocation("V"), 1, GL_FALSE, identity);
         glUniformMatrix4fv(gpuProgram.GetLocation("P"), 1, GL_FALSE, glm::value_ptr(projectionMatrix));
         glUniform4fv(gpuProgram.GetLocation("U_AmbientLightColor"), 1, ambientLightColor);
         glUniform4fv(gpuProgram.GetLocation("U_AmbientMaterial"), 1, ambientMaterial);
         glUniform4fv(gpuProgram.GetLocation("U_DiffuseLightColor"), 1, diffuseLightColor);
         glUniform4fv(gpuProgram.GetLocation("U_DiffuseMaterial"), 1, diffuseMaterial);
         glUniform4fv(gpuProgram.GetLocation("U_SpecularLightColor"), 1, specularLightColor);
         glUniform4fv(gpuProgram.GetLocation("U_SpecularMaterial"), 1, specularMaterial);
         glUniform3fv(gpuProgram.GetLocation("U_EyePos"), 1, eyePos);
         glUniform4fv(gpuProgram.GetLocation("U_LightDirection"), 1, spotLightDirection);
         glUniform1f(gpuProgram.GetLocation("U_DiffuseIntensity"), diffuseIntensity);
         //设置方向光光源的位置
         lightPos[0] = 0.0f;
         lightPos[1] = 1.5f;
         lightPos[2] = 0.0f;
         lightPos[3] = 0.0f;
         //漫反射光照强度
         diffuseIntensity = 1.0f;
         //聚光灯中心线和入射光线最大夹角
         spotLightCutoff = 0.0f;
         //设置shader中变量的值
         glUniform4fv(gpuProgram.GetLocation("U_LightPos"), 1, lightPos);
         glUniform1f(gpuProgram.GetLocation("U_DiffuseIntensity"), diffuseIntensity);
         glUniform1f(gpuProgram.GetLocation("U_Cutoff"), spotLightCutoff);
         glUniformMatrix4fv(gpuProgram.GetLocation("M"), 1, GL_FALSE, glm::value_ptr(model1));
         glUniformMatrix4fv(gpuProgram.GetLocation("NM"), 1, GL_FALSE, glm::value_ptr(normalMatrix1));
         //绘制被方向光照射的立方体
         cube.Bind(gpuProgram.GetLocation("pos"), gpuProgram.GetLocation("texcoord"), gpuProgram.GetLocation("normal"));
         cube.Draw();
         //设置点光源的位置
         lightPos[0] = 0.0f;
         lightPos[1] = 3.0f;
         lightPos[2] = -6.0f;
         lightPos[3] = 1.0f;
         diffuseIntensity = 3.0f;
         //设置shader中变量的值
         glUniform4fv(gpuProgram.GetLocation("U_LightPos"), 1, lightPos);
         glUniform1f(gpuProgram.GetLocation("U_DiffuseIntensity"), diffuseIntensity);
         glUniformMatrix4fv(gpuProgram.GetLocation("M"), 1, GL_FALSE, glm::value_ptr(model2));
         glUniformMatrix4fv(gpuProgram.GetLocation("NM"), 1, GL_FALSE, glm::value_ptr(normalMatrix2));
         //绘制被点光源照射的立方体
         cube.Bind(gpuProgram.GetLocation("pos"), gpuProgram.GetLocation("texcoord"), gpuProgram.GetLocation("normal"));
         cube.Draw();
         //设置聚光灯的位置
         lightPos[0] = 2.0f;
         lightPos[1] = 3.0f;
         lightPos[2] = -6.0f;
         lightPos[3] = 1.0f;
         diffuseIntensity = 4.0f;
         spotLightCutoff = 15.0f;//degree
         glUniform4fv(gpuProgram.GetLocation("U_LightPos"), 1, lightPos);
         glUniform1f(gpuProgram.GetLocation("U_DiffuseIntensity"), diffuseIntensity);
         glUniform1f(gpuProgram.GetLocation("U_Cutoff"), spotLightCutoff);
         glUniformMatrix4fv(gpuProgram.GetLocation("M"), 1, GL_FALSE, glm::value_ptr(model3));
         glUniformMatrix4fv(gpuProgram.GetLocation("NM"), 1, GL_FALSE, glm::value_ptr(normalMatrix3));
         //绘制被聚光灯照射的立方体
         cube.Bind(gpuProgram.GetLocation("pos"), gpuProgram.GetLocation("texcoord"), gpuProgram.GetLocation("normal"));
         cube.Draw();
         glUseProgram(0);
         glFlush();
         fbo.Unbind();


         glClearColor(0.1f, 0.4f, 0.7f, 1.0f);
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);//这步很重要
         glUseProgram(fsqProgram.mProgram);

         glActiveTexture(GL_TEXTURE0);
         //将fbo中的内容作为纹理
         glBindTexture(GL_TEXTURE_2D,fbo.GetBuffer("color"));
         glUniform1i(fsqProgram.GetLocation("U_MainTexture"), 0);

         if (isFullScreen){ //分屏渲染
             fsq.DrawToLeftTop(fsqProgram.GetLocation("pos"), fsqProgram.GetLocation("texcoord"));
             fsq.DrawToLeftBottom(fsqProgram.GetLocation("pos"), fsqProgram.GetLocation("texcoord"));
             fsq.DrawToRightTop(fsqProgram.GetLocation("pos"), fsqProgram.GetLocation("texcoord"));
             fsq.DrawToRightBottom(fsqProgram.GetLocation("pos"), fsqProgram.GetLocation("texcoord"));
         }
         else //绘制一个充满屏幕的四边形
         {
             fsq.Draw(fsqProgram.GetLocation("pos"), fsqProgram.GetLocation("texcoord"));
         }
         glUseProgram(0);
         glFlush();
         SwapBuffers(dc);
     }
     return 0;
 }