CODEWITHSUNDEEP
pythonopenglmultitexturing
BPL
BPL

Reputation: 9863

Multitexturing not working as expected

Given the below snippet:

import os
import textwrap

from OpenGL.GL import *
from OpenGL.GLU import *
from OpenGL.GLUT import *
from PIL import Image

from OpenGL.GL.ARB.multitexture import *
from OpenGL.extensions import alternate


def get_opengl_info():
    return textwrap.dedent("""\
        Vendor: {0}
        Renderer: {1}
        OpenGL Version: {2}
        Shader Version: {3}
        {4:*^80}
        Num Extensions: {5}
        {6}
    """).format(
        glGetString(GL_VENDOR).decode("utf-8"),
        glGetString(GL_RENDERER).decode("utf-8"),
        glGetString(GL_VERSION).decode("utf-8"),
        glGetString(GL_SHADING_LANGUAGE_VERSION).decode("utf-8"),
        "OPENGL EXTENSIONS",
        glGetIntegerv(GL_NUM_EXTENSIONS),
        "\n".join(glGetString(GL_EXTENSIONS).decode("utf-8").split())
    )


def create_gl_texture(use_active_texture, channel, width, height, pbits):
    id_texture = glGenTextures(1)
    if use_active_texture:
        glActiveTexture(GL_TEXTURE0 + channel)
    glBindTexture(GL_TEXTURE_2D, id_texture)
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1)
    glTexImage2D(GL_TEXTURE_2D, 0, 3, width, height, 0,
                 GL_RGBA, GL_UNSIGNED_BYTE, pbits)
    glTexParameter(
        GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR)
    glTexParameter(
        GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR)
    glTexParameter(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT)
    glTexParameter(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT)
    glGenerateMipmap(GL_TEXTURE_2D)

    return id_texture


def load_texture(use_active_texture, filename, i):
    image = Image.open(filename)
    ix = image.size[0]
    iy = image.size[1]
    pbits = image.convert("RGBA").tobytes("raw", "RGBA")

    id_texture = create_gl_texture(use_active_texture, i, ix, iy, pbits)
    print("Loaded", id_texture)
    return id_texture


X_AXIS = 0.0
Y_AXIS = 0.0
Z_AXIS = 0.0
DIRECTION = 1
id_textures = []


def init_gl(Width, Height):
    global glMultiTexCoord2f, glActiveTexture
    print(get_opengl_info())

    print("Choosing between: ", glMultiTexCoord2f.__name__,
          glMultiTexCoord2fARB.__name__)
    print("Choosing between: ", glActiveTexture.__name__,
          glActiveTextureARB.__name__)

    glMultiTexCoord2f = alternate(
        glMultiTexCoord2f,
        glMultiTexCoord2fARB
    )
    glActiveTexture = alternate(
        glActiveTexture,
        glActiveTextureARB,
    )

    print("Selected: ", glMultiTexCoord2f.__name__)
    print("Selected: ", glActiveTexture.__name__)

    if not glMultiTexCoord2f:
        print('Multitexture not supported!')
        sys.exit(1)

    glClearColor(0.0, 0.0, 0.0, 0.0)
    glClearDepth(1.0)
    glDepthFunc(GL_LESS)
    glEnable(GL_DEPTH_TEST)
    glShadeModel(GL_SMOOTH)
    glMatrixMode(GL_PROJECTION)
    glLoadIdentity()
    gluPerspective(45.0, float(Width) / float(Height), 0.1, 100.0)
    glMatrixMode(GL_MODELVIEW)
    glEnable(GL_TEXTURE_2D)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST)
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL)


def keyPressed(*args):
    if args[0] == "\033":
        sys.exit()

# Method0: Using glBindTexture + glTexCoord2f per face
def draw_method_0():
    global X_AXIS, Y_AXIS, Z_AXIS
    global DIRECTION
    global id_textures
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

    glLoadIdentity()
    glTranslatef(0.0, 0.0, -6.0)

    glRotatef(X_AXIS, 1.0, 0.0, 0.0)
    glRotatef(Y_AXIS, 0.0, 1.0, 0.0)
    glRotatef(Z_AXIS, 0.0, 0.0, 1.0)

    glBindTexture(GL_TEXTURE_2D, id_textures[0])
    glBegin(GL_QUADS)
    glTexCoord2f(0.0, 0.0)
    glVertex3f(-1.0, -1.0,  1.0)
    glTexCoord2f(1.0, 0.0)
    glVertex3f(1.0, -1.0,  1.0)
    glTexCoord2f(1.0, 1.0)
    glVertex3f(1.0,  1.0,  1.0)
    glTexCoord2f(0.0, 1.0)
    glVertex3f(-1.0,  1.0,  1.0)
    glEnd()

    glBindTexture(GL_TEXTURE_2D, id_textures[1])
    glBegin(GL_QUADS)
    glTexCoord2f(1.0, 0.0)
    glVertex3f(-1.0, -1.0, -1.0)
    glTexCoord2f(1.0, 1.0)
    glVertex3f(-1.0,  1.0, -1.0)
    glTexCoord2f(0.0, 1.0)
    glVertex3f(1.0,  1.0, -1.0)
    glTexCoord2f(0.0, 0.0)
    glVertex3f(1.0, -1.0, -1.0)
    glEnd()

    glBindTexture(GL_TEXTURE_2D, id_textures[2])
    glBegin(GL_QUADS)
    glTexCoord2f(0.0, 1.0)
    glVertex3f(-1.0,  1.0, -1.0)
    glTexCoord2f(0.0, 0.0)
    glVertex3f(-1.0,  1.0,  1.0)
    glTexCoord2f(1.0, 0.0)
    glVertex3f(1.0,  1.0,  1.0)
    glTexCoord2f(1.0, 1.0)
    glVertex3f(1.0,  1.0, -1.0)
    glEnd()

    glBindTexture(GL_TEXTURE_2D, id_textures[3])
    glBegin(GL_QUADS)
    glTexCoord2f(1.0, 1.0)
    glVertex3f(-1.0, -1.0, -1.0)
    glTexCoord2f(0.0, 1.0)
    glVertex3f(1.0, -1.0, -1.0)
    glTexCoord2f(0.0, 0.0)
    glVertex3f(1.0, -1.0,  1.0)
    glTexCoord2f(1.0, 0.0)
    glVertex3f(-1.0, -1.0,  1.0)
    glEnd()

    glBindTexture(GL_TEXTURE_2D, id_textures[4])
    glBegin(GL_QUADS)
    glTexCoord2f(1.0, 0.0)
    glVertex3f(1.0, -1.0, -1.0)
    glTexCoord2f(1.0, 1.0)
    glVertex3f(1.0,  1.0, -1.0)
    glTexCoord2f(0.0, 1.0)
    glVertex3f(1.0,  1.0,  1.0)
    glTexCoord2f(0.0, 0.0)
    glVertex3f(1.0, -1.0,  1.0)
    glEnd()

    glBindTexture(GL_TEXTURE_2D, id_textures[5])
    glBegin(GL_QUADS)
    glTexCoord2f(0.0, 0.0)
    glVertex3f(-1.0, -1.0, -1.0)
    glTexCoord2f(1.0, 0.0)
    glVertex3f(-1.0, -1.0,  1.0)
    glTexCoord2f(1.0, 1.0)
    glVertex3f(-1.0,  1.0,  1.0)
    glTexCoord2f(0.0, 1.0)
    glVertex3f(-1.0,  1.0, -1.0)
    glEnd()

    X_AXIS = X_AXIS - 0.030
    Z_AXIS = Z_AXIS - 0.030

    glutSwapBuffers()


# Method1: Using glActiveTexture+glBindTexture+glMultiTexCoord2f per face
def draw_method_1():
    global X_AXIS, Y_AXIS, Z_AXIS
    global DIRECTION
    global id_textures
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

    glLoadIdentity()
    glTranslatef(0.0, 0.0, -6.0)

    glRotatef(X_AXIS, 1.0, 0.0, 0.0)
    glRotatef(Y_AXIS, 0.0, 1.0, 0.0)
    glRotatef(Z_AXIS, 0.0, 0.0, 1.0)

    glActiveTexture(GL_TEXTURE0 + 0)
    glBindTexture(GL_TEXTURE_2D, id_textures[0])
    glBegin(GL_QUADS)
    glMultiTexCoord2f(GL_TEXTURE0 + 0, 0.0, 0.0)
    glVertex3f(-1.0, -1.0,  1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 0, 1.0, 0.0)
    glVertex3f(1.0, -1.0,  1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 0, 1.0, 1.0)
    glVertex3f(1.0,  1.0,  1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 0, 0.0, 1.0)
    glVertex3f(-1.0,  1.0,  1.0)
    glEnd()

    glActiveTexture(GL_TEXTURE0 + 1)
    glBindTexture(GL_TEXTURE_2D, id_textures[1])
    glBegin(GL_QUADS)
    glMultiTexCoord2f(GL_TEXTURE0 + 1, 1.0, 0.0)
    glVertex3f(-1.0, -1.0, -1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 1, 1.0, 1.0)
    glVertex3f(-1.0,  1.0, -1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 1, 0.0, 1.0)
    glVertex3f(1.0,  1.0, -1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 1, 0.0, 0.0)
    glVertex3f(1.0, -1.0, -1.0)
    glEnd()

    glActiveTexture(GL_TEXTURE0 + 2)
    glBindTexture(GL_TEXTURE_2D, id_textures[2])
    glBegin(GL_QUADS)
    glMultiTexCoord2f(GL_TEXTURE0 + 2, 0.0, 1.0)
    glVertex3f(-1.0,  1.0, -1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 2, 0.0, 0.0)
    glVertex3f(-1.0,  1.0,  1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 2, 1.0, 0.0)
    glVertex3f(1.0,  1.0,  1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 2, 1.0, 1.0)
    glVertex3f(1.0,  1.0, -1.0)
    glEnd()

    glActiveTexture(GL_TEXTURE0 + 3)
    glBindTexture(GL_TEXTURE_2D, id_textures[3])
    glBegin(GL_QUADS)
    glMultiTexCoord2f(GL_TEXTURE0 + 3, 1.0, 1.0)
    glVertex3f(-1.0, -1.0, -1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 3, 0.0, 1.0)
    glVertex3f(1.0, -1.0, -1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 3, 0.0, 0.0)
    glVertex3f(1.0, -1.0,  1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 3, 1.0, 0.0)
    glVertex3f(-1.0, -1.0,  1.0)
    glEnd()

    glActiveTexture(GL_TEXTURE0 + 4)
    glBindTexture(GL_TEXTURE_2D, id_textures[4])
    glBegin(GL_QUADS)
    glMultiTexCoord2f(GL_TEXTURE0 + 4, 1.0, 0.0)
    glVertex3f(1.0, -1.0, -1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 4, 1.0, 1.0)
    glVertex3f(1.0,  1.0, -1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 4, 0.0, 1.0)
    glVertex3f(1.0,  1.0,  1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 4, 0.0, 0.0)
    glVertex3f(1.0, -1.0,  1.0)
    glEnd()

    glActiveTexture(GL_TEXTURE0 + 5)
    glBindTexture(GL_TEXTURE_2D, id_textures[5])
    glBegin(GL_QUADS)
    glMultiTexCoord2f(GL_TEXTURE0 + 5, 0.0, 0.0)
    glVertex3f(-1.0, -1.0, -1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 5, 1.0, 0.0)
    glVertex3f(-1.0, -1.0,  1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 5, 1.0, 1.0)
    glVertex3f(-1.0,  1.0,  1.0)
    glMultiTexCoord2f(GL_TEXTURE0 + 5, 0.0, 1.0)
    glVertex3f(-1.0,  1.0, -1.0)
    glEnd()

    X_AXIS = X_AXIS - 0.030
    Z_AXIS = Z_AXIS - 0.030

    glutSwapBuffers()

# Method2: Using glActiveTexture+glBindTexture+glTexCoord2f per face
def draw_method_2():
    global X_AXIS, Y_AXIS, Z_AXIS
    global DIRECTION
    global id_textures
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

    glLoadIdentity()
    glTranslatef(0.0, 0.0, -6.0)

    glRotatef(X_AXIS, 1.0, 0.0, 0.0)
    glRotatef(Y_AXIS, 0.0, 1.0, 0.0)
    glRotatef(Z_AXIS, 0.0, 0.0, 1.0)

    glActiveTexture(GL_TEXTURE0 + 0)
    glBindTexture(GL_TEXTURE_2D, id_textures[0])
    glBegin(GL_QUADS)
    glTexCoord2f(0.0, 0.0)
    glVertex3f(-1.0, -1.0,  1.0)
    glTexCoord2f(1.0, 0.0)
    glVertex3f(1.0, -1.0,  1.0)
    glTexCoord2f(1.0, 1.0)
    glVertex3f(1.0,  1.0,  1.0)
    glTexCoord2f(0.0, 1.0)
    glVertex3f(-1.0,  1.0,  1.0)
    glEnd()

    glActiveTexture(GL_TEXTURE0 + 1)
    glBindTexture(GL_TEXTURE_2D, id_textures[1])
    glBegin(GL_QUADS)
    glTexCoord2f(1.0, 0.0)
    glVertex3f(-1.0, -1.0, -1.0)
    glTexCoord2f(1.0, 1.0)
    glVertex3f(-1.0,  1.0, -1.0)
    glTexCoord2f(0.0, 1.0)
    glVertex3f(1.0,  1.0, -1.0)
    glTexCoord2f(0.0, 0.0)
    glVertex3f(1.0, -1.0, -1.0)
    glEnd()

    glActiveTexture(GL_TEXTURE0 + 2)
    glBindTexture(GL_TEXTURE_2D, id_textures[2])
    glBegin(GL_QUADS)
    glTexCoord2f(0.0, 1.0)
    glVertex3f(-1.0,  1.0, -1.0)
    glTexCoord2f(0.0, 0.0)
    glVertex3f(-1.0,  1.0,  1.0)
    glTexCoord2f(1.0, 0.0)
    glVertex3f(1.0,  1.0,  1.0)
    glTexCoord2f(1.0, 1.0)
    glVertex3f(1.0,  1.0, -1.0)
    glEnd()

    glActiveTexture(GL_TEXTURE0 + 3)
    glBindTexture(GL_TEXTURE_2D, id_textures[3])
    glBegin(GL_QUADS)
    glTexCoord2f(1.0, 1.0)
    glVertex3f(-1.0, -1.0, -1.0)
    glTexCoord2f(0.0, 1.0)
    glVertex3f(1.0, -1.0, -1.0)
    glTexCoord2f(0.0, 0.0)
    glVertex3f(1.0, -1.0,  1.0)
    glTexCoord2f(1.0, 0.0)
    glVertex3f(-1.0, -1.0,  1.0)
    glEnd()

    glActiveTexture(GL_TEXTURE0 + 4)
    glBindTexture(GL_TEXTURE_2D, id_textures[4])
    glBegin(GL_QUADS)
    glTexCoord2f(1.0, 0.0)
    glVertex3f(1.0, -1.0, -1.0)
    glTexCoord2f(1.0, 1.0)
    glVertex3f(1.0,  1.0, -1.0)
    glTexCoord2f(0.0, 1.0)
    glVertex3f(1.0,  1.0,  1.0)
    glTexCoord2f(0.0, 0.0)
    glVertex3f(1.0, -1.0,  1.0)
    glEnd()

    glActiveTexture(GL_TEXTURE0 + 5)
    glBindTexture(GL_TEXTURE_2D, id_textures[5])
    glBegin(GL_QUADS)
    glTexCoord2f(0.0, 0.0)
    glVertex3f(-1.0, -1.0, -1.0)
    glTexCoord2f(1.0, 0.0)
    glVertex3f(-1.0, -1.0,  1.0)
    glTexCoord2f(1.0, 1.0)
    glVertex3f(-1.0,  1.0,  1.0)
    glTexCoord2f(0.0, 1.0)
    glVertex3f(-1.0,  1.0, -1.0)
    glEnd()

    X_AXIS = X_AXIS - 0.030
    Z_AXIS = Z_AXIS - 0.030

    glutSwapBuffers()

def load_textures(use_active_texture):
    global id_textures

    id_textures.append(load_texture(use_active_texture, "tex00.jpg", 0))
    id_textures.append(load_texture(use_active_texture, "tex01.jpg", 1))
    id_textures.append(load_texture(use_active_texture, "tex02.jpg", 2))
    id_textures.append(load_texture(use_active_texture, "tex03.jpg", 3))
    id_textures.append(load_texture(use_active_texture, "tex04.jpg", 4))
    id_textures.append(load_texture(use_active_texture, "tex05.jpg", 5))


def main():
    glutInit(sys.argv)
    glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_ALPHA | GLUT_DEPTH)
    glutInitWindowSize(640, 480)
    glutInitWindowPosition(200, 200)

    glutCreateWindow(b'OpenGL Python Textured Cube')

    init_gl(640, 480)

    current_method = 2
    draw_methods = {
        0: {"f": draw_method_0, "use_active_texture": False},
        1: {"f": draw_method_1, "use_active_texture": True},
        2: {"f": draw_method_2, "use_active_texture": True}
    }
    draw = draw_methods[current_method]["f"]
    load_textures(draw_methods[current_method]["use_active_texture"])
    glutDisplayFunc(draw)
    glutIdleFunc(draw)
    glutKeyboardFunc(keyPressed)

    glutMainLoop()

if __name__ == "__main__":
    main()

If i set current_method=0 I'll get the output I expect, all cube faces will use a different texture (as intended):

enter image description here

If i set current_method=1 only one face will be textured properly, that's a wrong output:

enter image description here

If i set current_method=2 all faces will be textured with the same texture[0], which is also a wrong output:

enter image description here

I'd like to understand why methods 1 & 2 are not giving the same output as method 0. I know when using shaders using glActiveTexture properly becomes trivial but I'd like to understand what's wrong when using these methods on the old fixed pipeline.

Upvotes: 0

Views: 766

Answers (2)

derhass
derhass

Reputation: 45322

If i set current_method=1 only one face will be textured properly, that's a wrong output.

No, this is not a wrong output. This is the perfectly correct output. You never set up your fixed function pipeline state to do any multitexturing (see @Dietrich Epp's answer for the details). What your render pipeline is configured to is just:

  • take the color value of the per-fragment interpolated vertex color (which you never set, iirc the default is white)
  • sample the texture which is currently bound to texture unit 0 with the per-fragment interpolated texture coords for texture coordinate set 0
  • blend the results together using the texture's alpha channel (GL_DECAL mode)
  • use that as the final fragment color.

So it is clear that you will never see anything from textures bound to the texture units > 0. So what do you see?

When current_method==0, you see what you expect.

If current_method==1, you see a single sample taken from the first texture - which is bound on unit 0 all the time. Since you do not set any tex coords for unit 0, the GL will just repeat the most recently set value, which is (0,1) for the last vertex of your first face. This will of course be used for all vertices of the new faces, so the interpolation will yield a constant value, resulting in a constant texture sampling result, resulting in a constant color.

Now with current_method=2 you still have the first texture bound at texture 0 for all faces. But since you now supply proper per-vertex texcoords for texture unit 0 again, sampling it will actually sample the texture at different regions again, so you'll get a sane mapping of that texture to the primitives.

Upvotes: 1

Dietrich Epp
Dietrich Epp

Reputation: 213308

I think the core issue here is a misunderstanding of how multitexturing works.

Multitexturing applies multiple textures at the same time to the same primitives. You want to apply different textures, one texture at a time, to different primitives. It should be clear from this that multitexturing does not do what you want, so there is no point in using it.

How multitexturing works

With multitexturing, multiple texture units combine their results using blending blending functions.

texture unit 0 --> +---------+
                   |  blend  | --\
texture unit 1 --> +---------+    \--> +---------+
                                       |  blend  | --> etc.
texture unit 2 ----------------------> +---------+

The blending function for each stage is set by glTexEnv and can be something like GL_MODULATE, GL_DECAL, or GL_ADD. This is how lightmaps were combined with textures back in the day: one texture would have the diffuse texture, and one texture would have the lightmap texture.

Again, this is completely different from the effect which you want to achieve, so multitexturing has no point in your application.

How glActiveTexture works

glActiveTexture doesn't change which texture unit is drawn to the screen. By default, only texture unit #0 will draw to the screen.

glActiveTexture just allows you to bind textures to other texture units. However, since texture unit #1 isn't being used, it doesn't matter what texture is bound to unit #1 or what the coordinates are. So you should always be using glActiveTexture(GL_TEXTURE0), since you always want to change texture unit #0.

Solutions

So, you have working code that doesn't use multitexturing. Great! You're done. You don't get bonus points for using more OpenGL features.

Alternatively, you could draw the entire cube in a single draw call if you use a 2D array texture. You simply load your existing textures as planes in a 2D array texture and use 3D texture coordinates instead of 2D texture coordinates. Again, no multitexturing required.

Upvotes: 2

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