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 <windows.h>
#include "glew.h"
#include <stdio.h>
#include <math.h>
#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;
}