Pyglet将文本绘制为纹理

Question

I'm trying to render an image with OpenGL using Pyglet. So far I've been able to setup the framebuffer and texture, render into it and save it as a PNG image. But I can't find out how to use Pyglets font rendering.

import numpy as np
import pyglet
from pyglet.gl import *
from ctypes import byref, sizeof, POINTER

width = 800
height = 600
cpp = 4

# Create the framebuffer (rendering target).
buf = gl.GLuint(0)
glGenFramebuffers(1, byref(buf))
glBindFramebuffer(GL_FRAMEBUFFER, buf)

# Create the texture (internal pixel data for the framebuffer).
tex = gl.GLuint(0)
glGenTextures(1, byref(tex))
glBindTexture(GL_TEXTURE_2D, tex)
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_FLOAT, None)

# Bind the texture to the framebuffer.
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, tex, 0)

# Something may have gone wrong during the process, depending on the
# capabilities of the GPU.
res = glCheckFramebufferStatus(GL_FRAMEBUFFER)
if res != GL_FRAMEBUFFER_COMPLETE:
  raise RuntimeError('Framebuffer not completed')

glViewport(0, 0, width, height)

# DRAW BEGIN
# =====================
glClearColor(0.1, 0.1, 0.1, 1.0)
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glColor3f(1.0, 0.5, 0.02)
glRectf(-0.75, -0.75, 0.75, 0.75)

glColor3f(1.0, 1.0, 1.0)
label = pyglet.text.Label(
  "Hello, World", font_name='Times New Roman', font_size=36,
  x=0, y=0, anchor_x='center', anchor_y='center')
label.draw()
# =====================
# DRAW END

# Read the buffer contents into a numpy array.
data = np.empty((height, width, cpp), dtype=np.float32)
glReadPixels(0, 0, width, height, GL_RGBA, GL_FLOAT, data.ctypes.data_as(POINTER(GLfloat)))

# Save the image.
import imageio
data = np.uint8(data * 255)
imageio.imwrite("foo.png", data)

The text does not appear on the framebuffer. How can I render the label on the framebuffer?

Answer 1

For rendering labels in Pyglet, first, an orthographic projection should be set up. In the given example, do it as follows:

glMatrixMode(GL_PROJECTION)
glLoadIdentity()
glOrtho(0, width, 0, height, -1, 1)
glMatrixMode(GL_MODELVIEW)
glLoadIdentity()
glColor3f(1.0, 1.0, 1.0)
label = pyglet.text.Label(
  "Hello, World", font_name='Times New Roman', font_size=36,
  x=width/2, y=height/2, anchor_x='center', anchor_y='center')
label.draw()

Then, the label is rendered as expected. (Note: moved the label's offset to the image center, ie x=width/2, y=height/2, )

foo.png (output framebuffer image)