This script will create a Texture containing a Ring image, then it will project this on some green cubes ("project" as in "overhead projector", not as in "flat projection"). This is usually called "projective Texturing". The secret in this is the GLSL Function texture2DProj, which does nothing more than to divide by the (usually useless) last Texture coordinate. Be careful however, as, since if you specify a vec4, the homogenous fourth coordinate, which is constant, will be used. Then you'd get a Projection without perspective.
Try using "GL_REPEAT" for the projected texture's wrapping, it looks fun.
The Distance measurement between projector and projection actually is a little clumsy, i bet there's a better way, but this one works so far.
# Pygame/PyopenGL example by Bastiaan Zapf, May 2009
#
# Projective Textures
#
# Employed techniques:
#
# - Vertex and Fragment shaders
# - Display Lists
# - Texturing
from OpenGL.GL import *
from OpenGL.GLU import *
import random
from math import * # trigonometry
import numpy
import pygame # just to get a display
import Image
import sys
import time
# get an OpenGL surface
pygame.init()
pygame.display.set_mode((800,600), pygame.OPENGL|pygame.DOUBLEBUF)
def jpg_file_write(name, number, data):
im = Image.frombuffer("RGBA", (800,600), data, "raw", "RGBA", 0, 0)
fnumber = "%05d" % number
im.save(name + fnumber + ".jpg")
# Create and Compile a shader
# but fail with a meaningful message if something goes wrong
def createAndCompileShader(type,source):
shader=glCreateShader(type)
glShaderSource(shader,source)
glCompileShader(shader)
# get "compile status" - glCompileShader will not fail with
# an exception in case of syntax errors
result=glGetShaderiv(shader,GL_COMPILE_STATUS)
if (result!=1): # shader didn't compile
raise Exception("Couldn't compile shader\nShader compilation Log:\n"+glGetShaderInfoLog(shader))
return shader
vertex_shader=createAndCompileShader(GL_VERTEX_SHADER,"""
varying vec3 normal, lightDir;
void main()
{
normal = gl_NormalMatrix * gl_Normal;
vec4 posEye = gl_ModelViewMatrix * gl_Vertex;
// Put World coordinates of Vertex, multiplied by TextureMatrix[0]
// into TexCoord[0]
gl_TexCoord[0] = gl_TextureMatrix[0]*gl_ModelViewMatrix*gl_Vertex;
// LightSource[0] position is assumed to be the projector position
lightDir = vec3(gl_LightSource[0].position.xyz - posEye.xyz);
gl_Position = gl_ProjectionMatrix * gl_ModelViewMatrix * gl_Vertex;
}
""");
fragment_shader=createAndCompileShader(GL_FRAGMENT_SHADER,"""
uniform sampler2D projMap;
varying vec3 normal, lightDir;
void main (void)
{
vec4 final_color = vec4(0.0,0.5,0,0.3);
vec3 N = normalize(normal);
vec3 L = normalize(lightDir);
float lambert = dot(N,L);
if( gl_TexCoord[0].z>0.0 // in front of projector?
&&
lambert>0 ) // facing projector?
{
// project texture - see notes for pitfall
vec4 ProjMapColor = texture2DProj(projMap, gl_TexCoord[0].xyz);
final_color += ProjMapColor*lambert*pow(length(L),-2.0);
}
gl_FragColor = final_color;
}
""");
# build shader program
program=glCreateProgram()
glAttachShader(program,vertex_shader)
glAttachShader(program,fragment_shader)
glLinkProgram(program)
# try to activate/enable shader program
# handle errors wisely
try:
glUseProgram(program)
except OpenGL.error.GLError:
print glGetProgramInfoLog(program)
raise
done = False
t=0
# load a cube into a display list
glNewList(1,GL_COMPILE)
glBegin(GL_QUADS)
glColor3f(1,1,1)
glNormal3f(0,0,-1)
glVertex3f( -1, -1, -1)
glVertex3f( 1, -1, -1)
glVertex3f( 1, 1, -1)
glVertex3f( -1, 1, -1)
glNormal3f(0,0,1)
glVertex3f( -1, -1, 1)
glVertex3f( 1, -1, 1)
glVertex3f( 1, 1, 1)
glVertex3f( -1, 1, 1)
glNormal3f(0,-1,0)
glVertex3f( -1, -1, -1)
glVertex3f( 1, -1, -1)
glVertex3f( 1, -1, 1)
glVertex3f( -1, -1, 1)
glNormal3f(0,1,0)
glVertex3f( -1, 1, -1)
glVertex3f( 1, 1, -1)
glVertex3f( 1, 1, 1)
glVertex3f( -1, 1, 1)
glNormal3f(-1,0,0)
glVertex3f( -1, -1, -1)
glVertex3f( -1, 1, -1)
glVertex3f( -1, 1, 1)
glVertex3f( -1, -1, 1)
glNormal3f(1,0,0)
glVertex3f( 1, -1, -1)
glVertex3f( 1, 1, -1)
glVertex3f( 1, 1, 1)
glVertex3f( 1, -1, 1)
glEnd()
glEndList()
texture=glGenTextures( 1 )
glActiveTexture(GL_TEXTURE0); # use first texturing unit
glBindTexture( GL_TEXTURE_2D, texture );
glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE );
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,
GL_CLAMP ); # try GL_REPEAT for fun
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,
GL_CLAMP );
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,
GL_LINEAR)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
GL_LINEAR)
texdata=numpy.zeros((256,256,4))
# a ring-shaped projection texture
for i in range(0,256):
x=(i-128.1)/128.0
for j in range(0,256):
y=(j-128.1)/128.0
if ((x*x+y*y>0.9) | (x*x+y*y<0.3)):
texdata[i][j][0]=0
texdata[i][j][1]=0
texdata[i][j][2]=0
texdata[i][j][3]=0
else:
texdata[i][j][0]=1
texdata[i][j][1]=1
texdata[i][j][2]=1
texdata[i][j][3]=1
glTexImage2Df(GL_TEXTURE_2D, 0,GL_RGBA,0,GL_RGBA,
texdata)
loc=glGetUniformLocation(program,"projMap");
glUniform1i(loc, 0) # use first texturing unit in shader
glEnable(GL_DEPTH_TEST)
while not done:
t=t+1
# Projector position and angle - this is rather rough so far
ppos=[sin(t/260.0)*4,cos(t/240.0)*4,0]
palpha=t
pbeta=t/3.0
# the texture matrix stores the intended projection
# however, signs seem to be reversed. This somehow makes sense, as
# we're transforming the texture coordinates
glMatrixMode(GL_TEXTURE);
glLoadIdentity()
glRotate(-palpha,0,1,0);
glRotate(-pbeta ,0,0,1);
glTranslate(-ppos[0],-ppos[1],-ppos[2])
# set light source position
glLightfv(GL_LIGHT0,GL_POSITION,[ppos[0],ppos[1],ppos[2]]);
# Set view
glMatrixMode(GL_PROJECTION)
glLoadIdentity()
gluPerspective(90,1,0.01,1000)
gluLookAt(sin(t/200.0)*8,sin(t/500.0)*3+8,cos(t/200.0)*8,0,0,0,0,1,0)
glClearColor(0.0, 0.0, 0.0, 1.0)
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT)
glMatrixMode(GL_MODELVIEW)
# draw a triangle to visualize the projector
# i don't have a clue how to relate the angles correctly here
glLoadIdentity()
glTranslate(ppos[0],ppos[1],ppos[2])
glBegin(GL_TRIANGLES)
glVertex3f(1,0,0)
glVertex3f(0,1,0)
glVertex3f(0,0,1)
glEnd()
# fallback
glColor3f(1,1,1)
glLoadIdentity()
# render a range of cubes
for i in range(-1,2):
for j in range(-1,2):
for k in range(-1,2):
glPushMatrix()
glTranslate(i*5,j*5,k*5)
glScale(1,1,1)
glCallList(1)
glPopMatrix()
time.sleep(0.01);
pygame.display.flip()
