CODEWITHSUNDEEP
pythonopengltexture-mappingpyopenglcolor-blending
jonathan topf
jonathan topf

Reputation: 8367

pyopengl set multipass texture blending mode

im trying to get multi texturing working and have so far got miltiple textures to load using this function

def loadTexture(name):

    img = PIL.Image.open(name) # .jpg, .bmp, etc. also work
    img_data = numpy.array(list(img.getdata()), numpy.int8)

    id = glGenTextures(1)
    glPixelStorei(GL_UNPACK_ALIGNMENT,1)
    glBindTexture(GL_TEXTURE_2D, id)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR)
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, img.size[0], img.size[1], 0, GL_RGB, GL_UNSIGNED_BYTE, img_data)
    return id

And I can set the texture to use with this code 

glBindTexture(GL_TEXTURE_2D, 1)
glEnable(GL_TEXTURE_2D)

My first attempt has been this:

glBindTexture(GL_TEXTURE_2D, 1)
glEnable(GL_TEXTURE_2D)
glBegin(GL_TRIANGLES)
....
glEnd()

glBindTexture(GL_TEXTURE_2D, 3)
glEnable(GL_TEXTURE_2D)
glBegin(GL_TRIANGLES)
....
glEnd()

So i render the polys twice and select a different texture each time, this seems to work in as much as calling glBindTexture(GL_TEXTURE_2D, n) will select the relivant texture and it will render but there is no blending going on per se, i just see the last selected texture in the render. I've tried adding glEnable(GL_BLEND), but that doesn't seem to do anything.

What I would like to do is to add pixels of the two passes together

How would I go about this?

Upvotes: 1

Views: 910

Answers (1)

kloffy
kloffy

Reputation: 2928

Are you sure that you need multiple passes? Here is an example of plain old OpenGL multitexturing:

import pygame
from pygame.locals import *

import numpy
import numpy.linalg

from OpenGL.GL import *
from OpenGL.GL.shaders import *

RESOLUTION = (800,600)

POSITIONS = numpy.array([[-1.0, -1.0], [+1.0, -1.0], [-1.0, +1.0], [+1.0, +1.0]], dtype=numpy.float32)
TEXCOORDS = numpy.array([[0.0, 1.0], [1.0, 1.0], [0.0, 0.0], [1.0, 0.0]], dtype=numpy.float32)

from PIL import Image

tex0 = 0
tex1 = 0

def loadTexture(path):
    img = Image.open(path)
    img = img.convert("RGBA") 
    img_data = numpy.array(list(img.getdata()), numpy.int8)

    texture = glGenTextures(1)
    glPixelStorei(GL_UNPACK_ALIGNMENT,1)
    glBindTexture(GL_TEXTURE_2D, texture)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR)
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, img.size[0], img.size[1], 0, GL_RGBA, GL_UNSIGNED_BYTE, img_data)

    return texture

def init():
    global tex0
    global tex1

    tex0 = loadTexture("texture0.png")
    tex1 = loadTexture("texture1.png")

    glViewport(0, 0, *RESOLUTION)

    aspect = RESOLUTION[0]/float(RESOLUTION[1])

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(-aspect, +aspect, -1.0, +1.0, -1.0, +1.0);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glClearColor(0.0, 0.0, 0.0, 1.0);

    glVertexPointer(2, GL_FLOAT, 0, POSITIONS);
    glEnableClientState(GL_VERTEX_ARRAY);

    glClientActiveTexture(GL_TEXTURE0);
    glTexCoordPointer(2, GL_FLOAT, 0, TEXCOORDS); 
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);

    glClientActiveTexture(GL_TEXTURE1);
    glTexCoordPointer(2, GL_FLOAT, 0, TEXCOORDS);
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);

def draw():
    glClear(GL_COLOR_BUFFER_BIT);

    glActiveTexture(GL_TEXTURE0);
    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, tex0);
    glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);

    glActiveTexture(GL_TEXTURE1);
    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, tex1);
    glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

def main():
    pygame.init()

    screen = pygame.display.set_mode(RESOLUTION, OPENGL | DOUBLEBUF)

    init()

    while True:
        for event in pygame.event.get():
            if event.type == QUIT: return

        draw()

        pygame.display.flip()

if __name__ == "__main__":
    main()

Have a look at Texture Combiners, they may enable the type of effect you are looking for. Of course, the state of the art for this kind of thing nowadays are shaders.

Upvotes: 2

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