CH7 Buffers and Blending

Pixel pipeline Vertex pipeline Course Map Transformation & Lighting Primitive assembly Viewport culling & clipping Texture blending Per Fragment operations Buffer operations Rasterizer setup Framebuffer We are here!

Topics Blending Fog Accumulation Buffer Stencil Buffer

Blending Example 1/6 #include #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_ALPHAAS/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 #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_STARTdefault : 0.0 GL_FOG_ENDdefault : 1.0 GL_FOG_INDEX default : 0.0 GL_FOG_COLORdefault : (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

ScreenAccumulation Buffer += return

Accumulation function void glAccum( GLenum op, GLfloat value ); operates on the accumulation buffer. op: The accumulation buffer operation. See next page. value: also see next page.

Accumulation function opMeaning GL_ACCUMread each pixel from the color buffer, multiplies the R, G, B, and alpha values by value, then add the result to accumulation buffer. GL_LOADthe same as GL_ACCUM, but replace the value in accumulation rather than add. GL_RETURNread values from the accumulation buffer, multiplies them by value, and places the result in the color buffers. GL_ADD / GL_MULTsimply 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 void GL_display() { // clear the buffer 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 = 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 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);

Stencil Buffer + Z Buffer

Z Buffer Test Stencil Buffer Test 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 paramMeaning 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 paramMeaning GL_KEEPkeep the current value GL_ZEROset the value in stencil buffer to zero GL_REPLACEset the value in stencil buffer to ref in glStencilFunc() GL_INCRincrease the current value in stencil buffer GL_DECRdecrease the current value in stencil buffer GL_INVERTbitwise 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 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 …