进给GL_POINTS时，几何着色器不执行任何操作

问题描述

我正在尝试使用几何着色器将点变成线段(GL_POINTS到GL_LINE_STRIP)，但是没有线段出现.如果我将输入更改为GL_LINES，然后重复顶点，那么我将获得期望的行为.发生了什么事?

I'm trying to use geometry shaders to turn points into line segments (GL_POINTS to GL_LINE_STRIP), but no line segments appear. If I change the input to GL_LINES, and just repeat the vertex, then I get the behavior I'm expecting. What's going on?

这是一个演示行为的完整程序.照原样，除了黑窗外，我什么也没有.将USE_POINTS设置为False会得到我期望的旋转的迷幻闪烁线.

Here's a complete program that demonstrates the behavior. As-is, I get nothing but a black window. Setting USE_POINTS to False gets me the rotating psychedelic flashing lines I'm expecting.

#!/usr/bin/python

from OpenGL.GL import *
from OpenGL.GLU import *
from OpenGL.GLUT import *
from OpenGL.GL.ARB.geometry_shader4 import *
from OpenGL.GL.EXT.geometry_shader4 import *

import Image
import numpy
import numpy.linalg as linalg
import random
from math import sin, cos

shader = None

USE_POINTS = True

def update(*args):
    glutTimerFunc(33, update, 0)
    glutPostRedisplay()

def display():
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

    t = glutGet(GLUT_ELAPSED_TIME)
    rot = t % (10 * 1000)
    theta = 2 * 3.141592 * (rot / 10000.0)

    glLoadIdentity()
    gluLookAt(-10*sin(theta), -10*cos(theta),   0,
                0,   0,   0,
                0,   0,   1)

    glUseProgram(shader)
    glUniform1f(glGetUniformLocation(shader, "distance"), rot/10000.0)

    # difference #1
    glBegin(GL_POINTS if USE_POINTS else GL_LINES)
    for x in [-2.5, 0, 2.5]:
        for y in [-2.5, 0, 2.5]:
            glVertexAttrib1f(7, random.uniform(0.0, 1.0))
            glVertexAttrib3f(0, x, y, 0)
            # difference #2
            if not USE_POINTS:
                glVertexAttrib1f(7, random.uniform(0.0, 1.0))
                glVertexAttrib3f(0, x, y, 0)
    glEnd()
    glUseProgram(0)

    glutSwapBuffers()

def key(*args):
    if args[0] == '\x1b':
        sys.exit(0);

def reshape(width, height):
    aspect = float(width)/float(height) if (height>0) else 1.0
    glViewport(0, 0, width, height)

    glMatrixMode(GL_PROJECTION)
    glLoadIdentity()

    gluPerspective(45.0,
                   aspect,
                   1.0, 100.0)

    glMatrixMode(GL_MODELVIEW)
    glLoadIdentity()

    glutPostRedisplay()

glutInit([])
glutInitDisplayString("rgba>=8 depth>16 double")
glutInitWindowSize(1280, 720)
glutCreateWindow("Geometry Shader")

glutDisplayFunc(display)
glutReshapeFunc(reshape)
glutKeyboardFunc(key)

glutTimerFunc(33, update, 0)

glEnable(GL_DEPTH_TEST)
glEnable(GL_POINT_SMOOTH)
glEnable(GL_LINE_SMOOTH)

shader = glCreateProgram()
vertex_shader = glCreateShader(GL_VERTEX_SHADER)
geometry_shader = glCreateShader(GL_GEOMETRY_SHADER)
fragment_shader = glCreateShader(GL_FRAGMENT_SHADER)

# difference #3
glProgramParameteriEXT(shader, GL_GEOMETRY_INPUT_TYPE_ARB, GL_POINTS if USE_POINTS else GL_LINES)
glProgramParameteriEXT(shader, GL_GEOMETRY_OUTPUT_TYPE_ARB, GL_LINE_STRIP)
glProgramParameteriEXT(shader, GL_GEOMETRY_VERTICES_OUT_ARB, 200)

glAttachShader(shader, vertex_shader)
glAttachShader(shader, geometry_shader)
glAttachShader(shader, fragment_shader)

glShaderSource(vertex_shader, """
attribute float color;
varying float geom_color;
void main(void) {
  gl_Position = gl_Vertex;
  geom_color = color;
}
""")
glCompileShader(vertex_shader)
print glGetShaderInfoLog(vertex_shader)

glShaderSource(geometry_shader, """
#version 120
#extension GL_EXT_geometry_shader4 : enable

varying in float geom_color[1];
varying out float frag_color;

uniform float distance;

void main(void)
{
 int x, y;

 for(x=-1; x<=1; x+=1) {
   for(y=-1; y<=1; y+=1) {
     gl_Position = gl_PositionIn[0];
     gl_Position.x += x * distance;
     gl_Position.y += y * distance;
     gl_Position.z -= 2.0;
     gl_Position = gl_ModelViewProjectionMatrix * gl_Position;
     frag_color = geom_color[0];
     EmitVertex();

     gl_Position = gl_PositionIn[0];
     gl_Position.x += x * distance;
     gl_Position.y += y * distance;
     gl_Position.z += 2.0;
     gl_Position = gl_ModelViewProjectionMatrix * gl_Position;
     frag_color = geom_color[0];
     EmitVertex();
     EndPrimitive();
   }
 }
}
""")
glCompileShader(geometry_shader)
print glGetShaderInfoLog(geometry_shader)

glShaderSource(fragment_shader, """
varying float frag_color;
void main(void) {
  gl_FragColor = vec4(frag_color,1.0-frag_color,frag_color,1);
}
""")
glCompileShader(fragment_shader)
print glGetShaderInfoLog(fragment_shader)

glLinkProgram(shader)
print glGetProgramInfoLog(shader)

glBindAttribLocation(shader, 7, "color")

glLinkProgram(shader)
print glGetProgramInfoLog(shader)


glutMainLoop()

推荐答案

我使用GL_EXT_geometry_shader4规范对代码进行了交叉检查，至少看不到任何明显的错误.根据规范，所有输入图元都可以与所有类型的输出图元一起使用.如果OpenGL通过glGetError没有返回任何错误，并且没有着色器链接器/编译错误，那么我会说这是与ATI或pyOpenGL有关的问题.

I cross-checked the code with the GL_EXT_geometry_shader4 specification, and I don't see any obvious errors at least. According to the specification, all input primitives work with all types of output primitives. If OpenGL returns no errors via glGetError, and no shader linker/compilation errors, I'd say this is an ATI or pyOpenGL-related issue.

我相当确定我已经测试了几何着色器的大多数输入和输出原语组合，并且它们都可以在我的Nvidia卡上使用.我虽然使用本机C OpenGL库，但未使用绑定.

I'm fairly sure I've tested most combinations of input and output primitives for geometry shaders, and they all work on my Nvidia card. I use the native C OpenGL libraries though, not a binding.

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