CH7 Buffers and Blending

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();

Blending Example 2/6

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);glutDisplayFunc(display);glutReshapeFunc(reshape);glutIdleFunc(idle);glutMainLoop();return;

}

Blending Example 3/6

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(-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();

}

Blending Example 4/6

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);

Blending Example 5/6

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();

}

Blending Example 6/6

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(…,…)

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(…,…)

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 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();

}

Accumulation example 2/3

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();

}

Accumulation example 3/3

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();

}

Accumulation example 2 2/3

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, 50.0);glMatrixMode(GL_MODELVIEW);glLoadIdentity();

}

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();

}

Accumulation example 2 3/3

How to use accumulation buffer?

glutInitDisplayMode(GLUT_ACCUM);

glClear(GL_ACCUM_BUFFER_BIT);

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.)

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();

}

Stencil buffer example 2/3

void GL_reshape(GLsizei w, GLsizei h){

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);

}

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

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();

}

Stencil buffer example 3/3

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…

Stencil buffer + Z 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 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