Draw rectangle over texture OpenGL

问题

I'm using python 3 with pygame and OpenGL to try to accomplish what I thought it would be a simple task: Drawing a rectangle. The idea is to have a white rectangle over (or bellow) a transparent texture, but whenever I add the texture to the screen the rectangle vanishes, whether I render it before or after the texture.

Bellow is a sample code displaying the problem (you can add any Player1.png image of your choice, the problem will remain the same - at least in my computer)

import pygame
import sys
from OpenGL.GL import *
from pygame.locals import *

# set pygame screen
pygame.display.set_mode((500, 500), OPENGL | DOUBLEBUF)
info = pygame.display.Info()

# basic opengl configuration
glViewport(0, 0, info.current_w, info.current_h)
glDepthRange(0, 1)
glMatrixMode(GL_PROJECTION)
glMatrixMode(GL_MODELVIEW)
glLoadIdentity()
glShadeModel(GL_SMOOTH)
glClearColor(0.0, 0.0, 0.0, 0.0)
glClearDepth(1.0)
glDisable(GL_DEPTH_TEST)
glDisable(GL_LIGHTING)
glDepthFunc(GL_LEQUAL)
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST)
glEnable(GL_BLEND)

# load texture
surf = pygame.image.load('Player1.png')
s = pygame.image.tostring(surf, 'RGBA')
texID = glGenTextures(1)
glBindTexture(GL_TEXTURE_2D, texID)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP)
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 142, 65, 0, GL_RGBA, GL_UNSIGNED_BYTE, s)
glGenerateMipmap(GL_TEXTURE_2D)
glBindTexture(GL_TEXTURE_2D, 0)

# create pygame clock
MAINCLOCK = pygame.time.Clock()

# init screen
pygame.display.init()

while True:
    # get quit event
    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit()

    # prepare to render screen
    glClear(GL_COLOR_BUFFER_BIT)
    glLoadIdentity()
    glDisable(GL_LIGHTING)
    glEnable(GL_TEXTURE_2D)
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
    glClearColor(0, 0, 0, 1.0)

    # draw texture
    glBindTexture(GL_TEXTURE_2D, texID)
    glBegin(GL_QUADS)
    glTexCoord2f(0, 0); glVertex2f(-1, -1)
    glTexCoord2f(0, 1); glVertex2f(-1, 1)
    glTexCoord2f(1, 1); glVertex2f(1, 1)
    glTexCoord2f(1, 0); glVertex2f(1, -1)
    glEnd()

    # draw rectangle
    glColor3fv((1, 1, 1))
    glRectf(-1, 1, 0, 0.5)

    pygame.display.flip()
    MAINCLOCK.tick(60)

It most likely has to do something on how OpenGL treats Textures vs Rects, but I'm not sure what.

BTW: I know the image is upside down

Thanks in advance

回答1:

You have to enable two-dimensional texturing before you draw the texture, as you do it (glEnable(GL_TEXTURE_2D)).

But you have to disable two-dimensional texturing again, before you draw the rectangle:

# draw rectangle
glDisable(GL_TEXTURE_2D)
glColor3fv((1, 1, 1))
glRectf(-1, 1, 0, 0.5)

Note, the texture is still bound, when you draw the rectangle. Since you do not provide texture coordinates, when you draw the rectangle. This causes that the current texture coordinate is applied to the rectangle and a single texel is drawn all over the rectangle.

e.g. The last texture coordinate set was glTexCoord2f(1, 0):

Further note, if you would change the color for the rectangle, then the entire texture get tint by this color. If texturing is enabled, then by default the color of the texel is multiplied by the current color, because by default the texture environment mode (GL_TEXTURE_ENV_MODE) is GL_MODULATE. See glTexEnv.

glDisable(GL_TEXTURE_2D)
glColor3fv((1, 0, 0))    # red
glRectf(-1, 1, 0, 0.5)

Set the "white" color before you draw the texture:

glEnable(GL_TEXTURE_2D)
glColor3fv((1, 1, 1))

来源：https://stackoverflow.com/questions/49212051/draw-rectangle-over-texture-opengl

标签

python

python-3.x

opengl

pygame