CH7 Buffers and Blending

Pixel pipeline

Vertex pipeline

Course Map

Transformation&

Lighting

Primitiveassembly

Viewport culling&

clipping

Textureblending

Per Fragmentoperations

Bufferoperations

Rasterizersetup

Framebuffer

We are here!

Topics

Blending Fog Accumulation Buffer Stencil Buffer

Blending Example 1/6

#include <math.h>#include <time.h>#include "glut.h"

GLfloat alpha = 0.0;GLfloat pos[4] = {0, 10, 10, 0};GLfloat dif_l[4] = {1.0, 1.0, 1.0, 1.0};GLfloat dif_t[4] = {1.0, 0.5, 0.8, 1.0};GLfloat dif_m[4] = {0.5, 0.8, 0.8, cos(alpha)};

int time1,time2;

void display();void reshape(GLsizei, GLsizei);void idle();


void main(int argc, char** argv){glutInit(&argc, argv);glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);glutInitWindowSize (500, 500);glutCreateWindow("Blending");glEnable(GL_DEPTH_TEST);glEnable(GL_LIGHTING);glutDisplayFunc(display);glutReshapeFunc(reshape);glutIdleFunc(idle);glutMainLoop();return;

}


void reshape(GLsizei w, GLsizei h){glViewport(0, 0, 500, 500);glMatrixMode(GL_PROJECTION);glLoadIdentity();gluPerspective(45, 1 / 1, 0.1, 1000);glMatrixMode(GL_MODELVIEW);glLoadIdentity();gluLookAt(-10, 10, 30, 0, 0, 0, 0, 1, 0);

}void idle(){

time2 = clock();alpha += 3.14 *(time2-time1)/CLK_TCK;dif_m[3] = (cos(alpha) + 1) / 2;time1 = time2;glutPostRedisplay();

}


void display(){glClearColor(0, 0, 0, 0);glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);glEnable(GL_LIGHT0);glLightfv(GL_LIGHT0, GL_POSITION, pos);glLightfv(GL_LIGHT0, GL_DIFFUSE, dif_l);glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, dif_t);glutSolidTeapot(5);


glEnable(GL_BLEND);glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, dif_m);glBegin(GL_POLYGON);glNormal3f(0, 0, 1);glVertex3f(-5, -5, 10);glVertex3f(5, -5, 10);glVertex3f(5, 5, 10);glVertex3f(-5, 5, 10);glEnd();glutSwapBuffers();

}

Blend Function 1/2

glBlendFunc(GLenum sfactor, GLenum dfactor); Color = source_color * sfactor +

destination_color * dfactor

Blend Function 2/2

Parameter (f(R), f(G), f(B), f(A))

GL_ZERO (0,0,0,0)

GL_ONE (1,1,1,1)

GL_SRC_COLOR (RS/kR,GS/kG,BS/kB,AS/kA)

GL_ONE_MINUS_SRC_COLOR (1,1,1,1)-(RS/kR,GS/kG,BS/kB,AS/kA)

GL_DST_COLOR (Rd/kR,Gd/kG,Bd/kB,Ad/kA)

GL_ONE_MINUS_DST_COLOR (1,1,1,1)-(Rd/kR,Gd/kG,Bd/kB,Ad/kA)

GL_SRC_ALPHA AS/kA,AS/kA,AS/kA,AS/kA

GL_ONE_MINUS_SRC_ALPHA (1,1,1,1) -(AS/kA,AS/kA,AS/kA,AS/kA)

GL_DST_ALPHA (AD/kA,AD/kA,AD/kA,AD/kA)

GL_ONE_MINUS_DST_ALPHA (1,1,1,1) -(AD/kA,AD/kA,AD/kA,AD/kA)

How to Use Blending?

Remember to enable glEnable(GL_BLEND);

Set up blend function glBlendFunc(…,…)

Draw object

Fog Example 1/6

#include <gl/glaux.h>#include "glut.h"

GLfloat fcolor[4]={1.0, 1.0, 1.0, 1.0};AUX_RGBImageRec * img;GLuint texObject[1];

void LoadTexture(char* filename){img = auxDIBImageLoad(filename);glGenTextures(1, texObject);glBindTexture(GL_TEXTURE_2D, texObject[0]);glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, img->sizeX, img->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, img->data);glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);

}

Fog Example 2/6

void display(){glEnable(GL_FOG);glFogf(GL_FOG_MODE, GL_EXP);glFogf(GL_FOG_DENSITY, 0.5);glFogfv(GL_FOG_COLOR, fcolor);glClearColor(0, 0, 0, 0);glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);glEnable(GL_TEXTURE_2D);glBindTexture(GL_TEXTURE_2D, texObject[0]);

Fog Example 3/6

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();glFlush();glutSwapBuffers();

}

Fog Example 4/6

void reshape(GLsizei w, GLsizei h){glViewport(0, 0, 500, 500);glMatrixMode(GL_PROJECTION);glLoadIdentity();gluPerspective(45, 1 / 1, 0.1, 1000);glMatrixMode(GL_MODELVIEW);glLoadIdentity();gluLookAt(0.0, 0.5, 0.0, 50.0, 0.0, 50.0, 0.0, 1.0, 0.0);

}

Fog Example 5/6

void main(int argc, char** argv){glutInit(&argc, argv);glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);glutInitWindowSize (500, 500);glutCreateWindow("Blending");glEnable(GL_DEPTH_TEST);glEnable(GL_LIGHTING);LoadTexture("check.bmp");glutDisplayFunc(display);glutReshapeFunc(reshape);glutMainLoop();return;

}

Fog Example 6/6

Fog Function 1/2

glFog{f,i}[v]{GLenum pname, param}Pname param

GL_FOG_MODE GL_LINEAR, GL_EXP, GL_EXP2

GL_FOG_DENSITY default : 1.0

GL_FOG_START default : 0.0

GL_FOG_END default : 1.0

GL_FOG_INDEX default : 0.0

GL_FOG_COLOR default : (0,0,0,0)

Fog Function 2/2

GL_LINEAR

GL_EXP

GL_EXP2

COLOR:

How to Use Fog?

Remember to enable glEnable(GL_FOG);

Set up fog function glFogf(…,…)

Draw object

Buffers in OpenGL

Color Buffer Store the color value to be seen on

screen. Depth Buffer

Store the depth values for each pixel. Stencil Buffer Accumulation Buffer

Accumulation Buffer

Screen AccumulationBuffer

+=

return

Accumulation function void glAccum( GLenum op, GLfloat value ); operates on the accumulation buffer. http://msdn.microsoft.com/library/default.asp?url=/library/en-us/opengl/

glfunc01_8o4t.asp op: The accumulation buffer

operation. See next page. value: also see next page.

Accumulation functionop Meaning

GL_ACCUM read each pixel from the color buffer, multiplies the R, G, B, and alpha values by value, then add the result to accumulation buffer.

GL_LOAD the same as GL_ACCUM, but replace the value in accumulation rather than add.

GL_RETURN read values from the accumulation buffer, multiplies them by value, and places the result in the color buffers.

GL_ADD / GL_MULT simply add / multiply the values of each pixel in the accumulation buffer by value, and return to the accumulation buffer. (GL_MULT will clamp value from –1.0 to 1.0 while GL_ADD will not.)

Accumulation example 1/3

#include <GL/glut.h>void GL_display(){

// clear the bufferglClearColor(0.0, 0.0, 0.0, 0.0);glClearAccum(0.0, 0.0, 0.0, 0.0); glClear(GL_ACCUM_BUFFER_BIT);for(int i = 0; i < 360; i++){

glClear(GL_COLOR_BUFFER_BIT);glColor3f(1.0, 1 - (float)i / 180, 1 - (float)i / 360);glPushMatrix();glTranslatef(0, -6, -10);glRotatef(i,0, 1, 0);glutWireTeapot(5);glPopMatrix();glAccum(GL_ACCUM, 0.01);

}glAccum(GL_RETURN, 1.0) ;glutSwapBuffers();

}


void GL_reshape(GLsizei w, GLsizei h){

glViewport(0, 0, w, h);glMatrixMode(GL_PROJECTION);glLoadIdentity();gluPerspective(60.0, (GLfloat)w/(GLfloat)h, 1.0, 20.0);glMatrixMode(GL_MODELVIEW);glLoadIdentity();gluLookAt(0.0, 3.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

}

int main(int argc, char** argv){

glutInit(&argc, argv);glutInitWindowSize(500, 500);glutInitWindowPosition(0, 0);glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_ACCUM);glutCreateWindow("Accumulation");glutDisplayFunc(GL_display);glutReshapeFunc(GL_reshape);glutMainLoop();

}


Motion blur

Accumulation example 2 1/3

#include <GL/glut.h>

void GL_display(){

glClearColor(0.0, 0.0, 0.0, 0.0);glClearAccum(0.0, 0.0, 0.0, 0.0); glClear(GL_ACCUM_BUFFER_BIT);for(int i = 1; i <5; i++){

glClear(GL_COLOR_BUFFER_BIT);glLoadIdentity();gluLookAt(i * 0.4, 0.0, 8.0, i * 0.4, 0.0, 0.0, 0.0, 1.0, 0.0);glColor3f(1, 0, 0);glutWireTeapot(2);glAccum(GL_ACCUM, (float)i);

}glAccum(GL_RETURN, 0.1) ;glutSwapBuffers();

}



glViewport(0, 0, w, h);glMatrixMode(GL_PROJECTION);glLoadIdentity();gluPerspective(60.0, (GLfloat)w/(GLfloat)h, 1.0, 50.0);glMatrixMode(GL_MODELVIEW);glLoadIdentity();

}


glutInit(&argc, argv);glutInitWindowSize(500, 500);glutInitWindowPosition(0, 0);glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_ACCUM);glutCreateWindow("Accumulation");glutDisplayFunc(GL_display);glutReshapeFunc(GL_reshape);glutMainLoop();

}

How to use accumulation buffer?

glutInitDisplayMode(GLUT_ACCUM);

glClear(GL_ACCUM_BUFFER_BIT);

Stencil Buffer + Z Buffer

Stencil Buffer + Z Buffer

Z BufferTest

StencilBufferTest

Pixel

Pass

Fail

Screen

Pass Fail

Pass

Stencil Testing 1/2

void glStencilFunc( GLenum func, GLint ref, GLuint mask ); sets the function and reference value

for stencil testing. func: test function, see next page. ref: reference value mask:A mask that is ANDed with both

the reference value and the stored stencil value when the test is done.

Stencil Testing 2/2

param Meaning

GL_NEVER Always fails.

GL_LESS Passes if ( ref & mask) < ( stencil & mask).

GL_LEQUAL Passes if ( ref & mask) ≤ ( stencil & mask).

GL_GEQUAL Passes if ( ref & mask) ≥ ( stencil & mask).

GL_NOTEQUAL Passes if ( ref & mask) ( stencil & mask).

GL_ALWAYS Always passes.

Modify stencil buffer 1/2

void glStencilOp( GLenum fail, GLenum zfail, GLenum zpass ); sets the stencil test actions. fail: The action to take when the

stencil test fails zfail: Stencil action when the stencil

test passes, but the depth test fails. zpass: both the stencil test and the

depth test pass

Modify stencil buffer 2/2

param Meaning

GL_KEEP keep the current value

GL_ZERO set the value in stencil buffer to zero

GL_REPLACE set the value in stencil buffer to ref in glStencilFunc()

GL_INCR increase the current value in stencil buffer

GL_DECR decrease the current value in stencil buffer

GL_INVERT bitwise inverse the current value in stencil buffer

How to use stencil buffer?

1. glutInitDisplayMode(GLUT_STENCIL);

2. glEnable(GL_STENCIL_TEST);

3. glClearStencil(0);4. glClear(GL_STENCIL_BUFFER_BIT);

Stencil buffer example 1/3

#include<gl/glut.h>

void GL_display(){glEnable(GL_DEPTH_TEST);glEnable(GL_STENCIL_TEST);glClearStencil(0);glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);glStencilFunc(GL_ALWAYS, 1, 1);glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);glColor3f(0.0, 1.0, 1.0);glutSolidCube(16.0);glClear(GL_DEPTH_BUFFER_BIT);glStencilOp(GL_KEEP, GL_KEEP, GL_INVERT);glStencilFunc(GL_EQUAL, 1, 1);glColor3f(1.0, 1.0, 1.0);glutSolidTeapot(8);glFlush();

}



glViewport(0, 0, w, h);glMatrixMode(GL_PROJECTION);glLoadIdentity();gluPerspective(60.0, (GLfloat)w/(GLfloat)h, 0.5, 100.0);glMatrixMode(GL_MODELVIEW);glLoadIdentity();gluLookAt(0.0, 0.0, 50.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

}


glutInit(&argc, argv);glutInitWindowSize(400, 400);glutInitWindowPosition(0, 0);glutInitDisplayMode(GLUT_SINGLE | GLUT_RGBA | GLUT_DEPTH | GLUT_STENCIL);glutCreateWindow("Stencil Buffer");glutDisplayFunc(GL_display);glutReshapeFunc(GL_reshape);glutMainLoop();

}

Other example… 1/2

void GL_display(){glEnable(GL_DEPTH_TEST);glEnable(GL_STENCIL_TEST);glClearStencil(0);glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);glStencilFunc(GL_ALWAYS, 1, 1);glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);glColor3f(0.0, 1.0, 1.0);glutSolidCube(16.0);glClear(GL_DEPTH_BUFFER_BIT);glStencilOp(GL_KEEP, GL_KEEP, GL_INVERT);glStencilFunc(GL_EQUAL, 1, 1);glColor3f(1.0, 1.0, 1.0);glutSolidTeapot(8);glStencilFunc(GL_NOTEQUAL, 1, 1);glColor3f(1.0, 1.0, 0.0);glPushMatrix();glTranslatef(10, 0, 0);glutSolidSphere(12, 10, 6);glPopMatrix();glFlush();

}

Other example… 2/2

Cooler example…

CH7 Buffers and Blending

Documents

Transcript of CH7 Buffers and Blending