python - 使用 GLSL 的 OpenGL 阴影贴图

Question

我正在尝试使用 GLSL 使阴影贴图工作。不幸的是，即使我有相当不错的深度缓冲精度，我的深度渲染结果也无法使用。它像线框一样渲染，下图可能是更好的描述。

我还包括一个测试用例(包含着色器的单个文件)，唯一的依赖项是 pyopengl。

# shadow mapping test
# utkualtinkaya at gmail 
# shader is from http://www.fabiensanglard.net/shadowmapping/index.php

from OpenGL.GL import *
from OpenGL.GLU import * 
from OpenGL.GLUT import *
from OpenGL.GL.shaders import *
from OpenGL.GL.framebufferobjects import *
import math

class Camera:
    def __init__(self):
        self.rotx, self.roty = math.pi/4, math.pi/4
        self.distance = 100
        self.moving = False
        self.ex, self.ey = 0, 0
        self.size = (800, 600) 

    def load_matrices(self):
        glViewport(0, 0, *self.size)
        y = math.cos(self.roty) * self.distance
        x = math.sin(self.roty) * math.cos(self.rotx) * self.distance
        z = math.sin(self.roty) * math.sin(self.rotx) * self.distance

        glMatrixMode(GL_PROJECTION)
        glLoadIdentity()
        gluPerspective(45.0, self.size[0]/float(self.size[1]), 1, 1000)

        glMatrixMode(GL_MODELVIEW)
        glLoadIdentity()
        gluLookAt(x,y,z, 0,0,0, 0,1,0)

    def on_mouse_button (self, b, s, x, y):
        self.moving = not s
        self.ex, self.ey = x, y
        if b in [3, 4]:
            dz = (1 if b == 3 else -1)
            self.distance += self.distance/15.0 * dz;

    def on_mouse_move(self, x, y, z = 0):
        if self.moving:            
            self.rotx += (x-self.ex) / 300.0
            self.roty += -(y-self.ey) / 300.0
            self.ex, self.ey = x, y

    def set_size(self, w, h):
        self.size = w, h

class Shader():
    def __init__(self):
        self.is_built = False
        self.uniforms = {}

    def build(self):
        self.program = compileProgram(
        compileShader('''
            uniform mat4 camMatrix;
            uniform mat4 shadowMatrix;
            varying vec4 depthProjection;
            uniform bool useShadow;

            void main() {
                gl_Position = camMatrix * gl_ModelViewMatrix * gl_Vertex;
                depthProjection = shadowMatrix * gl_ModelViewMatrix * gl_Vertex;
                gl_FrontColor = gl_Color;
            }
        ''',GL_VERTEX_SHADER),
        compileShader('''
            varying vec4 depthProjection;
            uniform sampler2D shadowMap;
            uniform bool useShadow;

            void main () {
                float shadow = 1.0;
                if (useShadow) {
                    vec4 shadowCoord = depthProjection / depthProjection.w ;
                    // shadowCoord.z -= 0.0003;            
                    float distanceFromLight = texture2D(shadowMap, shadowCoord.st).z;                                
                    if (depthProjection .w > 0.0)
                        shadow = distanceFromLight < shadowCoord.z ? 0.5 : 1.0 ;            

                    }
                gl_FragColor = shadow * gl_Color;
              }
        ''',GL_FRAGMENT_SHADER),)
        self.is_built = True

        self.uniforms['camMatrix'] = glGetUniformLocation(self.program, 'camMatrix')
        self.uniforms['shadowMatrix'] = glGetUniformLocation(self.program, 'shadowMatrix')
        self.uniforms['shadowMap'] = glGetUniformLocation(self.program, 'shadowMap')
        self.uniforms['useShadow'] = glGetUniformLocation(self.program, 'useShadow')
        print self.uniforms

    def use(self):
        if not self.is_built:
            self.build()
        glUseProgram(self.program)

class Test:
    def __init__(self):
        glutInit(sys.argv)
        glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_ALPHA | GLUT_DEPTH)
        glutInitWindowSize(800, 600)
        glutInitWindowPosition(1120/2, 100)
        self.window = glutCreateWindow("Shadow Test")
        self.cam = Camera()
        self.light = Camera()
        self.cam.set_size(800, 600)
        self.light.set_size(2048, 2048)
        self.light.distance = 100
        self.shader = Shader()
        self.initialized = False        

    def setup(self):
        self.initialized = True
        glClearColor(0,0,0,1.0);
        glDepthFunc(GL_LESS)
        glEnable(GL_DEPTH_TEST)

        self.fbo = glGenFramebuffers(1);
        self.shadowTexture = glGenTextures(1)

        glBindFramebuffer(GL_FRAMEBUFFER, self.fbo)

        w, h = self.light.size

        glActiveTexture(GL_TEXTURE5)         
        glBindTexture(GL_TEXTURE_2D, self.shadowTexture)

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
        glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP );
        glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP );

        glTexImage2D( GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, w, h, 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_INT, None)

        glDrawBuffer(GL_NONE)
        glReadBuffer(GL_NONE)

        glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, self.fbo, 0)

        FBOstatus = glCheckFramebufferStatus(GL_FRAMEBUFFER)
        if FBOstatus != GL_FRAMEBUFFER_COMPLETE:
            print ("GL_FRAMEBUFFER_COMPLETE_EXT failed, CANNOT use FBO\n");

        glBindFramebuffer(GL_FRAMEBUFFER, 0)
        #glActiveTexture(GL_TEXTURE0)                

    def draw(self):
        glPushMatrix()
        glTranslate(0, 10 ,0)
        glColor4f(0, 1, 1, 1)
        glutSolidCube(5)
        glPopMatrix()

        glPushMatrix()
        glColor4f(0.5, 0.5, .5, 1)
        glScale(100, 1, 100)
        glutSolidCube(1)
        glPopMatrix()

    def apply_camera(self, cam):
        cam.load_matrices()
        model_view = glGetDoublev(GL_MODELVIEW_MATRIX);
        projection = glGetDoublev(GL_PROJECTION_MATRIX);
        glMatrixMode(GL_MODELVIEW)
        glLoadIdentity()
        glMultMatrixd(projection)
        glMultMatrixd(model_view)        
        glUniformMatrix4fv(self.shader.uniforms['camMatrix'], 1, False, glGetFloatv(GL_MODELVIEW_MATRIX))
        glLoadIdentity()     

    def shadow_pass(self):
        glUniform1i(self.shader.uniforms['useShadow'], 0)

        glBindFramebuffer(GL_FRAMEBUFFER, self.fbo)
        glClear(GL_DEPTH_BUFFER_BIT)
        glCullFace(GL_FRONT)
        self.apply_camera(self.light)        
        self.draw()
        glBindFramebuffer(GL_FRAMEBUFFER, 0)

    def final_pass(self):
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

        self.light.load_matrices()
        model_view = glGetDoublev(GL_MODELVIEW_MATRIX);
        projection = glGetDoublev(GL_PROJECTION_MATRIX);        
        glMatrixMode(GL_MODELVIEW)
        glLoadIdentity()
        bias = [ 0.5, 0.0, 0.0, 0.0, 
                 0.0, 0.5, 0.0, 0.0,
                 0.0, 0.0, 0.5, 0.0,
                 0.5, 0.5, 0.5, 1.0]
        glLoadMatrixd(bias)
        glMultMatrixd(projection)
        glMultMatrixd(model_view)
        glUniformMatrix4fv(self.shader.uniforms['shadowMatrix'], 1, False, glGetFloatv(GL_MODELVIEW_MATRIX))

        glActiveTexture(GL_TEXTURE5)
        glBindTexture(GL_TEXTURE_2D, self.shadowTexture)                
        glUniform1i(self.shader.uniforms['shadowMap'], 5)

        glUniform1i(self.shader.uniforms['useShadow'], 1);

        self.apply_camera(self.cam)
        glLoadIdentity()
        glCullFace(GL_BACK)
        self.draw()

    def render(self):
        if not self.initialized: self.setup()
        self.shader.use()        
        self.shadow_pass()
        self.final_pass()        
        glutSwapBuffers()

    def mouse_move(self, *args):
        self.cam.on_mouse_move(*args)
        self.light.on_mouse_move(*args)

    def mouse_button(self, b, *args):
        if b==0:
            self.light.on_mouse_button(b, *args)
        else:
            self.cam.on_mouse_button(b, *args)

    def main(self):
        glutDisplayFunc(self.render)
        glutIdleFunc(self.render)
        glutMouseFunc(self.mouse_button)
        glutMotionFunc(self.mouse_move)
        glutReshapeFunc(self.cam.set_size)
        #self.setup()
        glutMainLoop()

if __name__ == '__main__':
    test = Test()
    test.main()

Answer 1

解决了，这是绑定(bind)问题，在阴影 channel 片段着色器中，我只是检查了一个 bool 值以禁用读取纹理，但这还不够。我应该在阴影传递之前取消绑定(bind)纹理，这在文档中提到为:

引自 OpenGL 引用资料:需要采取特殊的预防措施，以避免在纹理对象当前绑定(bind)并可能被当前顶点或片段着色器采样时将纹理图像附加到当前绑定(bind)的帧缓冲区。

NVIDIA 忽略了这一点，ATI 的行为几乎如文档所述“未定义”。