在OpenGL窗口（python）中可视化单个字符

Question

在下面的代码中，我想在opengl窗口中显示一个字符，但如果该字符以小尺寸在水平和垂直方向上多次打印到一个空间中，我想，这个空间应该与该字符的大小一样大。多谢各位

代码（几乎全部）：

import numpy
from freetype import *
import OpenGL.GL as gl
import OpenGL.GLUT as glut

text  = 'H'

def makefont(filename, size):
    face = Face(filename)
    face.set_char_size( size*64 )
    face.load_char(text, FT_LOAD_RENDER | FT_LOAD_FORCE_AUTOHINT)
    bitmap = face.glyph.bitmap

    data = bitmap.buffer
    rows = bitmap.rows
    width = bitmap.width
    ascender  = face.glyph.bitmap_top
    descender = bitmap.rows-face.glyph.bitmap_top
    height = ascender+descender
    imageData = numpy.array(bitmap.buffer, numpy.uint8).reshape(rows,width)
    imageData = imageData[::-1,:]
    #########

    textureID = gl.glGenTextures(1)
    gl.glBindTexture( gl.GL_TEXTURE_2D, textureID )
    gl.glTexParameterf( gl.GL_TEXTURE_2D, gl.GL_TEXTURE_MAG_FILTER, gl.GL_LINEAR )
    gl.glTexParameterf( gl.GL_TEXTURE_2D, gl.GL_TEXTURE_MIN_FILTER, gl.GL_LINEAR )
    gl.glTexImage2D( gl.GL_TEXTURE_2D, 0, gl.GL_RGBA, width, height, 0,
                     gl.GL_RGBA, gl.GL_UNSIGNED_BYTE, imageData )
    #
    gl.glBindTexture(gl.GL_TEXTURE_2D, textureID)
    gl.glBegin(gl.GL_QUADS)
    gl.glTexCoord2f(0, 0)
    x = 0
    y = 0
    w = width
    h = height
    gl.glVertex2f(x, y)
    gl.glTexCoord2f(1, 0)
    gl.glVertex2f(x + w, y)
    gl.glTexCoord2f(1, 1)
    gl.glVertex2f(x + w, y + h)
    gl.glTexCoord2f(0, 1)
    gl.glVertex2f( x, y + h) 
    gl.glEnd()


def on_display( ):
    gl.glClearColor(1,1,1,1)
    gl.glClear(gl.GL_COLOR_BUFFER_BIT | gl.GL_DEPTH_BUFFER_BIT)
    gl.glColor(0,0,0,1)
    makefont( './VeraMono.ttf', 64 )
    glut.glutSwapBuffers( )

def on_reshape( width, height ):
    #

if __name__ == '__main__':
    import sys
    glut.glutInitDisplayMode( glut.GLUT_DOUBLE | glut.GLUT_RGB | glut.GLUT_DEPTH )

    gl.glTexEnvf( gl.GL_TEXTURE_ENV, gl.GL_TEXTURE_ENV_MODE, gl.GL_MODULATE )
    gl.glEnable( gl.GL_DEPTH_TEST )
    gl.glEnable( gl.GL_BLEND )
    gl.glEnable( gl.GL_COLOR_MATERIAL )
    gl.glColorMaterial( gl.GL_FRONT_AND_BACK, gl.GL_AMBIENT_AND_DIFFUSE )
    gl.glBlendFunc( gl.GL_SRC_ALPHA, gl.GL_ONE_MINUS_SRC_ALPHA )
    gl.glEnable( gl.GL_TEXTURE_2D )
    glut.glutMainLoop( )

Answer 1

freetype库渲染的glyph图像只有一个颜色通道。使用GL_ALPHA作为纹理的格式和内部格式。见^{}。
此外，还必须更改GL_UNPACK_ALIGNMENT参数。 ^{}参数定义从缓冲区读取图像时图像每行（行）中第一个像素的对齐方式。默认情况下，此参数为4。
字形图像的每个像素被编码在一个字节中，并且图像被紧密压缩。因此，字形图像的对齐为1，在读取图像和指定纹理之前，必须更改参数：

gl.glPixelStorei(gl.GL_UNPACK_ALIGNMENT, 1)
gl.glTexImage2D(gl.GL_TEXTURE_2D, 0, gl.GL_ALPHA, width, height, 0,
                gl.GL_ALPHA, gl.GL_UNSIGNED_BYTE, imageData)

---

由于未设置任何投影矩阵，因此必须在规格化设备空间中绘制几何体。在标准化设备空间中，所有坐标都在rage[-1.0,1.0]中：

x, y, w, h = -1, -1, 2, 2
gl.glBegin(gl.GL_QUADS)
gl.glTexCoord2f(0, 0)
gl.glVertex2f(x, y)
gl.glTexCoord2f(1, 0)
gl.glVertex2f(x + w, y)
gl.glTexCoord2f(1, 1)
gl.glVertex2f(x + w, y + h)
gl.glTexCoord2f(0, 1)
gl.glVertex2f( x, y + h) 
gl.glEnd()

---

如果要使用窗口坐标，则必须通过^{}设置正交投影：

gl.glMatrixMode(gl.GL_PROJECTION)
gl.glLoadIdentity()
gl.glOrtho(0, width, height, 0, -1, 1)
gl.glMatrixMode(gl.GL_MODELVIEW)

x, y, w, h = 0, 0, width, height
gl.glBegin(gl.GL_QUADS)
gl.glTexCoord2f(0, 0)
gl.glVertex2f(x, y)
gl.glTexCoord2f(1, 0)
gl.glVertex2f(x + w, y)
gl.glTexCoord2f(1, 1)
gl.glVertex2f(x + w, y + h)
gl.glTexCoord2f(0, 1)
gl.glVertex2f( x, y + h) 
gl.glEnd()

---

完成函数makefont和on_reshape：

def makefont(filename, size):
    face = Face(filename)
    face.set_char_size( size*64 )
    face.load_char(text, FT_LOAD_RENDER | FT_LOAD_FORCE_AUTOHINT)
    bitmap = face.glyph.bitmap

    data = bitmap.buffer
    rows = bitmap.rows
    width = bitmap.width
    ascender  = face.glyph.bitmap_top
    descender = bitmap.rows-face.glyph.bitmap_top
    height = ascender+descender
    imageData = numpy.array(bitmap.buffer, numpy.uint8).reshape(rows,width)
    imageData = imageData[::-1,:]

    textureID = gl.glGenTextures(1)
    gl.glBindTexture( gl.GL_TEXTURE_2D, textureID )
    gl.glTexParameterf( gl.GL_TEXTURE_2D, gl.GL_TEXTURE_MAG_FILTER, gl.GL_LINEAR )
    gl.glTexParameterf( gl.GL_TEXTURE_2D, gl.GL_TEXTURE_MIN_FILTER, gl.GL_LINEAR )
    gl.glPixelStorei(gl.GL_UNPACK_ALIGNMENT, 1)
    gl.glTexImage2D(gl.GL_TEXTURE_2D, 0, gl.GL_ALPHA, width, height, 0,
                gl.GL_ALPHA, gl.GL_UNSIGNED_BYTE, imageData)

    x, y, w, h = 0, 0, width, height
    gl.glBindTexture(gl.GL_TEXTURE_2D, textureID)
    gl.glBegin(gl.GL_QUADS)
    gl.glTexCoord2f(0, 0)
    gl.glVertex2f(x, y)
    gl.glTexCoord2f(1, 0)
    gl.glVertex2f(x + w, y)
    gl.glTexCoord2f(1, 1)
    gl.glVertex2f(x + w, y + h)
    gl.glTexCoord2f(0, 1)
    gl.glVertex2f( x, y + h) 
    gl.glEnd()

def on_reshape( width, height ):
    gl.glViewport(0, 0, width, height)
    gl.glMatrixMode(gl.GL_PROJECTION)
    gl.glLoadIdentity()
    gl.glOrtho(0, width, height, 0, -1, 1)
    gl.glMatrixMode(gl.GL_MODELVIEW)

另见Immediate mode and legacy OpenGL