CH8 Frame Buffer Object 1. Introduction Name OpenGL :Frame Buffer Object DirectX:Render Target Usage Render to Texture 2.

CH8 Frame Buffer Object

1

Introduction

Name OpenGL : Frame Buffer Object DirectX: Render Target

Usage Render to Texture

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Replace the Screen

PixelsScreen 0

User FBO 1

User FBO n

….

(Default)

Bind

ColorColor Attachment

0

Depth AttachmentDepth

Color Attachment 0

Color Attachment 1

gl_FragData[0]

gl_FragData[1]

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Functions Create and Destroy FBO

void glGenFramebuffersEXT(GLsizei n, GLuint* ids) void glDeleteFramebuffersEXT(GLsizei n, const

GLuint* ids)

Bind FBO void glBindFramebufferEXT(GLenum target, GLuint

id)

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Attachment

Texture Render Buffer

You cant send it to shader It supports some format that texture

doesn’t.

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Render Buffer Create

void glGenRenderbuffersEXT(GLsizei n, GLuint* ids);

Destroy void glDeleteRenderbuffersEXT(GLsizei n, const Gluint*

ids);

Bind void glBindRenderbufferEXT(GLenum target, GLuint id);

Storage void glRenderbufferStorageEXT(GLenum target,

GLenum internalFormat, GLsizei width, GLsizei height)

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Render Buffer Parameters Target

GL_RENDERBUFFER_EXT Internal Format

GL_RGB, GL_RGBA GL_DEPTH_COMPONENT16, 24, 32, 32F GL_DEPTH24_STENCIL8,

GL_DEPTH32F_STENCIL8. GL_STENCIL_INDEX, GL_STENCIL_INDEX8_EXT

(Does not recommend!)

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Attachment Points

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Attach Texture glFramebufferTexture2DEXT(GLenum target, GLenum

attachmentPoint, GLenum textureTarget, GLuint textureId, GLint level)

Target GL_FRAMEBUFFER_EXT

Attachment Point GL_COLOR_ATTACHMENT0_EXT ~ GL_COLOR_ATTACHMENTn_EXT GL_DEPTH_ATTACHMENT_EXT GL_STENCIL_ATTACHMENT_EXT

Texture Target GL_TEXTURE_2D or GL_TEXTURE_2D_ARRAY

Texture Id Set 0 to detach texture

Level The mipmap level of texture

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Attach Render Buffer void glFramebufferRenderbufferEXT(GLenum target,

GLenum attachmentPoint, GLenum renderbufferTarget, GLuint renderbufferId)

Target GL_FRAMEBUFFER_EXT

Attachment Point As same as texture

Render Buffer Target GL_RENDERBUFFER_EXT

Render Buffer Id Set 0 to detach render buffer

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Multiple Render Target void glDrawBuffers( GLsizei n, const GLenum

*bufs );

Call this function after binding anther FBO N

The number for render targets Buffers

The connection of gl_FragData[] to color attachment

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The example of buffer arrayGLenum iDrawBuffer[16] ={

GL_COLOR_ATTACHMENT0_EXT,GL_COLOR_ATTACHMENT1_EXT,GL_COLOR_ATTACHMENT2_EXT,GL_COLOR_ATTACHMENT3_EXT,

.

.

.

.GL_COLOR_ATTACHMENT15_EXT

};

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PixelShader

Color Attachment 0

Color Attachment 1

gl_FragData[0]

gl_FragData[1]

PixelShader

Color Attachment 0

Color Attachment 1

gl_FragData[0]

gl_FragData[1]

If you want …

Does Not Recommend!

GLenum iDrawBuffer[2] ={

GL_COLOR_ATTACHMENT1_EXT,GL_COLOR_ATTACHMENT0_EXT,

};glDrawBuffers(2, iDrawBuffer);

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Check FBO GLenum glCheckFramebufferStatusEXT(GLenum target)

Return Value Case GL_FRAMEBUFFER_COMPLETE_EXT : OK GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT_EXT GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT_E

XT GL_FRAMEBUFFER_INCOMPLETE_DIMENSIONS_EXT GL_FRAMEBUFFER_INCOMPLETE_FORMATS_EXT GL_FRAMEBUFFER_INCOMPLETE_DRAW_BUFFER_EXT GL_FRAMEBUFFER_INCOMPLETE_READ_BUFFER_EXT GL_FRAMEBUFFER_UNSUPPORTED_EXT

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Additional Information

Build Mipmap void glGenerateMipmap(GLenum

target); Get Texture Content

void glGetTexImage(GLenum target, GLint level, GLenum format, GLenum type, GLvoid * img);

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Example : Render To Texture

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Code#include <stdio.h>#include "glew.h"#include "glut.h“int g_iViewport[4];GLuint g_iFBO;GLuint g_iRB;GLuint g_iTexture;void init();void display();void reshape(GLsizei , GLsizei );void init();

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void reshape(GLsizei w, GLsizei h){g_iViewport[0] = 0;g_iViewport[1] = 0;g_iViewport[2] = w;g_iViewport[3] = h;

}

int main(int argc, char** argv){ glutInit(&argc, argv); glutInitWindowSize(512, 512); glutInitWindowPosition(0, 0); glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB); glutCreateWindow("FBO"); glewInit(); init(); glutDisplayFunc(display); glutReshapeFunc(reshape); glutMainLoop(); return 0;}

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void init(){

//generate textureglEnable(GL_TEXTURE_2D);glGenTextures(1, &g_iTexture);glBindTexture(GL_TEXTURE_2D, g_iTexture);glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA_FLOAT32_ATI, 512, 512,

0, GL_RGBA, GL_FLOAT, NULL);glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

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//generate render bufferglGenRenderbuffers(1, &g_iRB);glBindRenderbuffer(GL_RENDERBUFFER, g_iRB);glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT32, 512, 512);

//generate FBOglGenFramebuffers(1, &g_iFBO);glBindFramebuffer(GL_FRAMEBUFFER, g_iFBO);

//attachglFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, g_iRB);glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, g_iTexture, 0);

}

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void display(){

glClearColor(0.0f, 0.0f, 0.0f, 0.0f);glClearDepth(1.0f);

//Pass1{

//render to textureglBindFramebuffer(GL_FRAMEBUFFER, g_iFBO);//clear texture and render buffer in FBOglClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);glMatrixMode(GL_MODELVIEW);glLoadIdentity();glMatrixMode(GL_PROJECTION);glLoadIdentity();glOrtho(-1.0f, 1.0f, -1.0f, 1.0f, -1.0f, 1.0f);glViewport(g_iViewport[0], g_iViewport[1], g_iViewport[2],

g_iViewport[3]); 21

glBindTexture(GL_TEXTURE_2D, 0);glBegin(GL_QUADS);glColor3d(1.0f, 1.0f, 1.0f);glVertex3f(-1.0f, -1.0f, 0.0f);glColor3d(1.0f, 0.0f, 0.0f);glVertex3f(1.0f, -1.0f, 0.0f);glColor3d(0.0f, 1.0f, 0.0f);glVertex3f(1.0f, 1.0f, 0.0f);glColor3d(0.0f, 0.0f, 1.0f);glVertex3f(-1.0f, 1.0f, 0.0f);glEnd();glColor3f(1.0, 1.0, 1.0);glutSolidTeapot(0.5);

} 22

//Pass2{

//render to screenglBindFramebuffer(GL_FRAMEBUFFER, 0);

//clear screenglClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glMatrixMode(GL_PROJECTION);glLoadIdentity();gluPerspective(60.0, 1.0, 0.5, 100.0);glMatrixMode(GL_MODELVIEW);glLoadIdentity();gluLookAt(0.0, 0.5, 0.0, 50.0, 0.0, 50.0, 0.0, 1.0, 0.0);

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glEnable(GL_TEXTURE_2D);glBindTexture(GL_TEXTURE_2D, g_iTexture);glBegin(GL_QUADS);glTexCoord2f(0.0, 0.0);glVertex3f(-50.0, 0.0, 0.0);glTexCoord2f(0.0, 100.0);glVertex3f(-50.0, 0.0, 100.0);glTexCoord2f(100.0, 100.0);glVertex3f(50.0, 0.0, 100.0);glTexCoord2f(100.0, 0.0);glVertex3f(50.0, 0.0, 0.0);glEnd();

}

glutSwapBuffers();}

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