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(-2.0f, 0.0f, -6.0f)*glm::rotate(-30.0f,1.0f,1.0f,1.0f);
	glm::mat4 model2 = glm::translate(0.0f, 0.0f, -6.0f)*glm::rotate(-30.0f,1.0f,1.0f,1.0f);
	glm::mat4 model3 = glm::translate(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;
}