【OpenGL】FBO渲染到纹理案例

1、使用用户FBO通过一系列操作从相对于镜面的反向照相机开始渲染场景地形和旋转中的甜甜圈以及代表反向照相机的蓝色圆筒，将其渲染结果存储到mirrorTexture（FBO映射目标就是GL_COLOR_ATTACHMENT0 这个纹理捆绑点）

2、重置FBO后，再次从真正的照相机视角来绘制场景地形和旋转的甜甜圈以及绘制镜面，并镜面会判断照相机是否能看到镜面来决定是否渲染出镜面画面（即mirrorTexture)，若无法看到则渲染黑色镜面。

需要注意的是，虽然在第一步也渲染了场景，但此时的场景是输出到FBO上的，这个结果会缓存到mirrorTexture 它是由glDrawBuffers(1, fboBuffs)来指定给哪个捆绑点对应的纹理的，而第二步才真正渲染到屏幕上。

#pragma comment(lib, "gltools.lib")
#include <stdio.h>
#include <iostream>#include <GLTools.h>
#include <GLShaderManager.h>
#include <GLFrustum.h>
#include <GLBatch.h>
#include <GLMatrixStack.h>
#include <GLGeometryTransform.h>
#include <StopWatch.h>//#include <GL/glu.h>#ifdef __APPLE__
#include <glut/glut.h>
#else
#define FREEGLUT_STATIC
#include <GL/glut.h>
#endifstatic GLfloat vGreen[] = { 0.0f, 1.0f, 0.0f, 1.0f };
static GLfloat vBlue[] = { 0.0f, 0.0f, 1.0f, 1.0f };
static GLfloat vWhite[] = { 1.0f, 1.0f, 1.0f, 1.0f };
static GLfloat vBlack[] = { 0.0f, 0.0f, 0.0f, 1.0f };
static GLfloat vGrey[] = { 0.5f, 0.5f, 0.5f, 1.0f };
static GLfloat vLightPos[] = { -2.0f, 3.0f, -2.0f, 1.0f };
static const GLenum windowBuff[] = { GL_BACK_LEFT };
static const GLenum fboBuffs[] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1, GL_COLOR_ATTACHMENT2 };
static GLint mirrorTexWidth = 800;
static GLint mirrorTexHeight = 800;GLsizei  screenWidth;           // Desired window or desktop width
GLsizei  screenHeight;          // Desired window or desktop heightGLboolean bFullScreen;           // Request to run full screen
GLboolean bAnimated;            // Request for continual updatesGLShaderManager     shaderManager;          // Shader Manager
GLMatrixStack       modelViewMatrix;        // Modelview Matrix
GLMatrixStack       projectionMatrix;       // Projection Matrix
GLFrustum           viewFrustum;            // View Frustum
GLGeometryTransform transformPipeline;      // Geometry Transform Pipeline
GLFrame             cameraFrame;            // Camera frame
GLFrame             mirrorFrame;            // Mirror frameGLTriangleBatch      torusBatch;
GLTriangleBatch     sphereBatch;
GLTriangleBatch     cylinderBatch;
GLBatch             floorBatch;
GLBatch             mirrorBatch;
GLBatch             mirrorBorderBatch;GLuint              fboName;
GLuint              textures[1];
GLuint              mirrorTexture;
GLuint              depthBufferName;void DrawWorld(GLfloat yRot);
bool LoadBMPTexture(const char *szFileName, GLenum minFilter, GLenum magFilter, GLenum wrapMode);///
// Load in a BMP file as a texture. Allows specification of the filters and the wrap mode
bool LoadBMPTexture(const char *szFileName, GLenum minFilter, GLenum magFilter, GLenum wrapMode)
{GLbyte *pBits;GLint iWidth, iHeight;pBits = gltReadBMPBits(szFileName, &iWidth, &iHeight);if (pBits == NULL)return false;// Set Wrap modesglTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, wrapMode);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, wrapMode);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, minFilter);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, magFilter);glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, iWidth, iHeight, 0, GL_BGR, GL_UNSIGNED_BYTE, pBits);// Do I need to generate mipmaps?if (minFilter == GL_LINEAR_MIPMAP_LINEAR || minFilter == GL_LINEAR_MIPMAP_NEAREST || minFilter == GL_NEAREST_MIPMAP_LINEAR || minFilter == GL_NEAREST_MIPMAP_NEAREST)glGenerateMipmap(GL_TEXTURE_2D);return true;
}///
// OpenGL related startup code is safe to put here. Load textures, etc.
void SetupRC()
{GLenum err = glewInit();if (GLEW_OK != err){/* Problem: glewInit failed, something is seriously wrong. */fprintf(stderr, "Error: %s\n", glewGetErrorString(err));}// Initialze Shader ManagershaderManager.InitializeStockShaders();glEnable(GL_DEPTH_TEST);// BlackglClearColor(0.0f, 0.0f, 0.0f, 1.0f);gltMakeTorus(torusBatch, 0.4f, 0.15f, 35, 35);gltMakeSphere(sphereBatch, 0.1f, 26, 13);gltMakeCylinder(cylinderBatch, 0.3f, 0.2f, 1.0, 10, 10);GLfloat alpha = 0.25f;floorBatch.Begin(GL_TRIANGLE_FAN, 4, 1);floorBatch.Color4f(0.0f, 1.0f, 0.0f, alpha);floorBatch.MultiTexCoord2f(0, 0.0f, 0.0f);floorBatch.Normal3f(0.0, 1.0f, 0.0f);floorBatch.Vertex3f(-20.0f, -0.41f, 20.0f);floorBatch.Color4f(0.0f, 1.0f, 0.0f, alpha);floorBatch.MultiTexCoord2f(0, 10.0f, 0.0f);floorBatch.Normal3f(0.0, 1.0f, 0.0f);floorBatch.Vertex3f(20.0f, -0.41f, 20.0f);floorBatch.Color4f(0.0f, 1.0f, 0.0f, alpha);floorBatch.MultiTexCoord2f(0, 10.0f, 10.0f);floorBatch.Normal3f(0.0, 1.0f, 0.0f);floorBatch.Vertex3f(20.0f, -0.41f, -20.0f);floorBatch.Color4f(0.0f, 1.0f, 0.0f, alpha);floorBatch.MultiTexCoord2f(0, 0.0f, 10.0f);floorBatch.Normal3f(0.0, 1.0f, 0.0f);floorBatch.Vertex3f(-20.0f, -0.41f, -20.0f);floorBatch.End();mirrorBatch.Begin(GL_TRIANGLE_FAN, 4, 1);mirrorBatch.Color4f(1.0f, 0.0f, 0.0f, 1.0f);mirrorBatch.MultiTexCoord2f(0, 0.0f, 0.0f);mirrorBatch.Normal3f(0.0f, 1.0f, 0.0f);mirrorBatch.Vertex3f(-1.0f, 0.0f, 0.0f);mirrorBatch.Color4f(1.0f, 0.0f, 0.0f, 1.0f);mirrorBatch.MultiTexCoord2f(0, 1.0f, 0.0f);mirrorBatch.Normal3f(0.0f, 1.0f, 0.0f);mirrorBatch.Vertex3f(1.0f, 0.0f, 0.0f);mirrorBatch.Color4f(1.0f, 0.0f, 0.0f, 1.0f);mirrorBatch.MultiTexCoord2f(0, 1.0f, 1.0f);mirrorBatch.Normal3f(0.0f, 1.0f, 0.0f);mirrorBatch.Vertex3f(1.0f, 2.0f, 0.0f);mirrorBatch.Color4f(1.0f, 0.0f, 0.0f, 1.0f);mirrorBatch.MultiTexCoord2f(0, 0.0f, 1.0f);mirrorBatch.Normal3f(0.0f, 1.0f, 0.0f);mirrorBatch.Vertex3f(-1.0f, 2.0f, 0.0f);mirrorBatch.End();mirrorBorderBatch.Begin(GL_TRIANGLE_STRIP, 13);mirrorBorderBatch.Normal3f(0.0f, 0.0f, 1.0f);mirrorBorderBatch.Vertex3f(-1.0f, 0.1f, 0.01f);mirrorBorderBatch.Normal3f(0.0f, 0.0f, 1.0f);mirrorBorderBatch.Vertex3f(-1.0f, 0.0f, 0.01f);mirrorBorderBatch.Normal3f(0.0f, 0.0f, 1.0f);mirrorBorderBatch.Vertex3f(1.0f, 0.1f, 0.01f);mirrorBorderBatch.Normal3f(0.0f, 0.0f, 1.0f);mirrorBorderBatch.Vertex3f(1.0f, 0.0f, 0.01f);mirrorBorderBatch.Normal3f(0.0f, 0.0f, 1.0f);mirrorBorderBatch.Vertex3f(0.9f, 0.0f, 0.01f);mirrorBorderBatch.Normal3f(0.0f, 0.0f, 1.0f);mirrorBorderBatch.Vertex3f(1.0f, 2.0f, 0.01f);mirrorBorderBatch.Normal3f(0.0f, 0.0f, 1.0f);mirrorBorderBatch.Vertex3f(0.9f, 2.0f, 0.01f);mirrorBorderBatch.Normal3f(0.0f, 0.0f, 1.0f);mirrorBorderBatch.Vertex3f(1.0f, 1.9f, 0.01f);mirrorBorderBatch.Normal3f(0.0f, 0.0f, 1.0f);mirrorBorderBatch.Vertex3f(-1.0f, 2.f, 0.01f);mirrorBorderBatch.Normal3f(0.0f, 0.0f, 1.0f);mirrorBorderBatch.Vertex3f(-1.0f, 1.9f, 0.01f);mirrorBorderBatch.Normal3f(0.0f, 0.0f, 1.0f);mirrorBorderBatch.Vertex3f(-0.9f, 2.f, 0.01f);mirrorBorderBatch.Normal3f(0.0f, 0.0f, 1.0f);mirrorBorderBatch.Vertex3f(-1.0f, 0.0f, 0.01f);mirrorBorderBatch.Normal3f(0.0f, 0.0f, 1.0f);mirrorBorderBatch.Vertex3f(-0.9f, 0.0f, 0.01f);mirrorBorderBatch.End();glGenTextures(1, textures);glBindTexture(GL_TEXTURE_2D, textures[0]);LoadBMPTexture("marble.bmp", GL_LINEAR_MIPMAP_LINEAR, GL_LINEAR, GL_REPEAT);// Create and bind an FBOglGenFramebuffers(1, &fboName);glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fboName);// Create depth renderbufferglGenRenderbuffers(1, &depthBufferName);glBindRenderbuffer(GL_RENDERBUFFER, depthBufferName);glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT32, mirrorTexWidth, mirrorTexHeight);// Create the reflection textureglGenTextures(1, &mirrorTexture);glBindTexture(GL_TEXTURE_2D, mirrorTexture);glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, mirrorTexWidth, mirrorTexHeight, 0, GL_RGBA, GL_FLOAT, NULL);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);// Attach texture to first color attachment and the depth RBOglFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, mirrorTexture, 0);glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthBufferName);// Make sure all went wellgltCheckErrors();// Reset framebuffer bindingglBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
}///
// Do your cleanup here. Free textures, display lists, buffer objects, etc.
void ShutdownRC(void)
{// Make sure default FBO is boundglBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);glBindFramebuffer(GL_READ_FRAMEBUFFER, 0);// Cleanup texturesglActiveTexture(GL_TEXTURE0);glBindTexture(GL_TEXTURE_2D, 0);glDeleteTextures(1, &mirrorTexture);glDeleteTextures(1, textures);// Cleanup RBOsglDeleteRenderbuffers(1, &depthBufferName);// Cleanup FBOsglDeleteFramebuffers(1, &fboName);}///
// This is called at least once and before any rendering occurs. If the screen
// is a resizeable window, then this will also get called whenever the window
// is resized.
void ChangeSize(int nWidth, int nHeight)
{glViewport(0, 0, nWidth, nHeight);transformPipeline.SetMatrixStacks(modelViewMatrix, projectionMatrix);viewFrustum.SetPerspective(35.0f, float(nWidth) / float(nHeight), 1.0f, 100.0f);projectionMatrix.LoadMatrix(viewFrustum.GetProjectionMatrix());modelViewMatrix.LoadIdentity();// update screen sizesscreenWidth = nWidth;screenHeight = nHeight;
}///
// Update the camera based on user input, toggle display modes
//
void SpecialKeys(int key, int x, int y)
{float linear = 0.40f;float angular = float(m3dDegToRad(2.5f));if (key == GLUT_KEY_UP)cameraFrame.MoveForward(linear);if (key == GLUT_KEY_DOWN)cameraFrame.MoveForward(-linear);if (key == GLUT_KEY_LEFT)cameraFrame.RotateWorld(angular, 0.0f, 1.0f, 0.0f);if (key == GLUT_KEY_RIGHT)cameraFrame.RotateWorld(-angular, 0.0f, 1.0f, 0.0f);
}///
// Draw the scene
//
void DrawWorld(GLfloat yRot)
{M3DMatrix44f mCamera;modelViewMatrix.GetMatrix(mCamera);// Need light position relative to the CameraM3DVector4f vLightTransformed;m3dTransformVector4(vLightTransformed, vLightPos, mCamera);// Draw the light source as a small white unshaded spheremodelViewMatrix.PushMatrix();modelViewMatrix.Translatev(vLightPos);shaderManager.UseStockShader(GLT_SHADER_FLAT, transformPipeline.GetModelViewProjectionMatrix(), vWhite);sphereBatch.Draw();modelViewMatrix.PopMatrix();// Draw stuff relative to the cameramodelViewMatrix.PushMatrix();modelViewMatrix.Translate(0.0f, 0.2f, -2.5f);modelViewMatrix.Rotate(yRot, 0.0f, 1.0f, 0.0f);shaderManager.UseStockShader(GLT_SHADER_POINT_LIGHT_DIFF,modelViewMatrix.GetMatrix(),transformPipeline.GetProjectionMatrix(),vLightTransformed, vGreen, 0);torusBatch.Draw();modelViewMatrix.PopMatrix();
}///
// Render a frame. The owning framework is responsible for buffer swaps,
// flushes, etc.
void RenderScene(void)
{static CStopWatch animationTimer;float yRot = animationTimer.GetElapsedSeconds() * 60.0f;M3DVector3f vCameraPos;M3DVector3f vCameraForward;M3DVector3f vMirrorPos;M3DVector3f vMirrorForward;cameraFrame.GetOrigin(vCameraPos);cameraFrame.GetForwardVector(vCameraForward);// Set position of mirror frame (camera)vMirrorPos[0] = 0.0;vMirrorPos[1] = 0.1f;vMirrorPos[2] = -6.0f; // view pos is actually behind mirrormirrorFrame.SetOrigin(vMirrorPos);// Calculate direction of mirror frame (camera)// Because the position of the mirror is known relative to the origin// find the direction vector by adding the mirror offset to the vector// of the viewer-originvMirrorForward[0] = vCameraPos[0];vMirrorForward[1] = vCameraPos[1];vMirrorForward[2] = (vCameraPos[2] + 5);m3dNormalizeVector3(vMirrorForward);mirrorFrame.SetForwardVector(vMirrorForward);// first render from the mirrors perspectiveglBindFramebuffer(GL_DRAW_FRAMEBUFFER, fboName);glDrawBuffers(1, fboBuffs);glViewport(0, 0, mirrorTexWidth, mirrorTexHeight);// Draw scene from the perspective of the mirror cameramodelViewMatrix.PushMatrix();M3DMatrix44f mMirrorView;mirrorFrame.GetCameraMatrix(mMirrorView);modelViewMatrix.MultMatrix(mMirrorView);// Flip the mirror camera horizontally for the reflectionmodelViewMatrix.Scale(-1.0f, 1.0f, 1.0f);glBindTexture(GL_TEXTURE_2D, textures[0]); // MarbleglClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);shaderManager.UseStockShader(GLT_SHADER_TEXTURE_MODULATE, transformPipeline.GetModelViewProjectionMatrix(), vWhite, 0);floorBatch.Draw();DrawWorld(yRot);// Now draw a cylinder representing the viewerM3DVector4f vLightTransformed;modelViewMatrix.GetMatrix(mMirrorView);m3dTransformVector4(vLightTransformed, vLightPos, mMirrorView);modelViewMatrix.Translate(vCameraPos[0], vCameraPos[1] - 0.8f, vCameraPos[2] - 1.0f);modelViewMatrix.Rotate(-90.0f, 1.0f, 0.0f, 0.0f);shaderManager.UseStockShader(GLT_SHADER_POINT_LIGHT_DIFF,modelViewMatrix.GetMatrix(),transformPipeline.GetProjectionMatrix(),vLightTransformed, vBlue, 0);cylinderBatch.Draw();modelViewMatrix.PopMatrix();// Reset FBO. Draw world again from the real cameras perspectiveglBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);glDrawBuffers(1, windowBuff);glViewport(0, 0, screenWidth, screenHeight);modelViewMatrix.PushMatrix();M3DMatrix44f mCamera;cameraFrame.GetCameraMatrix(mCamera);modelViewMatrix.MultMatrix(mCamera);glBindTexture(GL_TEXTURE_2D, textures[0]); // MarbleglClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);shaderManager.UseStockShader(GLT_SHADER_TEXTURE_MODULATE, transformPipeline.GetModelViewProjectionMatrix(), vWhite, 0);floorBatch.Draw();DrawWorld(yRot);// Now draw the mirror surfacesmodelViewMatrix.PushMatrix();modelViewMatrix.Translate(0.0f, -0.4f, -5.0f);if (vCameraPos[2] > -5.0){glBindTexture(GL_TEXTURE_2D, mirrorTexture); // ReflectionshaderManager.UseStockShader(GLT_SHADER_TEXTURE_REPLACE, transformPipeline.GetModelViewProjectionMatrix(), 0);}else{// If the camera is behind the mirror, just draw blackshaderManager.UseStockShader(GLT_SHADER_FLAT, transformPipeline.GetModelViewProjectionMatrix(), vBlack);}mirrorBatch.Draw();shaderManager.UseStockShader(GLT_SHADER_FLAT, transformPipeline.GetModelViewProjectionMatrix(), vGrey);mirrorBorderBatch.Draw();modelViewMatrix.PopMatrix();modelViewMatrix.PopMatrix();// Do the buffer SwapglutSwapBuffers();// Do it againglutPostRedisplay();
}int main(int argc, char* argv[])
{screenWidth = 800;screenHeight = 600;bFullScreen = false;bAnimated = true;fboName = 0;depthBufferName = 0;gltSetWorkingDirectory(argv[0]);glutInit(&argc, argv);glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);glutInitWindowSize(screenWidth, screenHeight);glutCreateWindow("FBO Textures");glutReshapeFunc(ChangeSize);glutDisplayFunc(RenderScene);glutSpecialFunc(SpecialKeys);SetupRC();glutMainLoop();ShutdownRC();return 0;
}

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