使用 GLSL 的 OpenGL 阴影贴图

Question

我正在尝试使用 GLSL 进行阴影贴图。不幸的是，即使我有相当不错的深度缓冲区精度，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（包括着色器的单个文件），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

解决了它，这是绑定问题，在阴影传递片段着色器中，我只是检查了一个布尔值以禁用读取纹理，但这还不够。我应该在阴影传递之前取消绑定纹理，这在文档中提到：

引用自 OpenGL 参考：
需要采取特殊的预防措施，以避免在纹理对象当前已绑定并且可能由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”。

Answer 2

// shadowCoord.z -= 0.0003;

您注释掉的影子偏见可以解决您的 z-fight 问题。将其更改为某个值，例如 += 0.0005，您应该可以开始了。