OpenGL 阴影贴图

Posted 2023-02-22

【中文标题】OpenGL 阴影贴图

【英文标题】：OpenGL Shadow Map

【发布时间】：2013-04-01 09:18:15

【问题描述】：

我正在尝试做一个基本的阴影贴图，但由于某种原因，它不能正确渲染。

Video of the Problem

我使用平面着色器渲染房子：

int shadowMapWidth = WINDOW_SIZE_X * (int)SHADOW_MAP_RATIO;
int shadowMapHeight =  WINDOW_SIZE_Y * (int)SHADOW_MAP_RATIO;

// Rendering into the shadow texture.
glActiveTexture(GL_TEXTURE0);
CALL_GL(glBindTexture(GL_TEXTURE_2D, shadowTexture));
// Bind the framebuffer.
CALL_GL(glBindFramebuffer(GL_FRAMEBUFFER, shadowFBO));
//Clear it
CALL_GL(glClear(GL_DEPTH_BUFFER_BIT));
CALL_GL(glViewport(0, 0, shadowMapWidth, shadowMapHeight));
CALL_GL(glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE));
//Render stuff
flatShader.use();
flatShader["baseColor"] = glm::vec4(1.0f,1.0f,1.0f,1.0f);
flatShader["pvm"] = projectionMatrix*pointLight.viewMatrix*cursor.modelMatrix;
cursor.draw(); //binds the vao and draws

// Revert for the scene.
CALL_GL(glBindFramebuffer(GL_FRAMEBUFFER, 0));
CALL_GL(glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE));
CALL_GL(glViewport(0, 0, WINDOW_SIZE_X, WINDOW_SIZE_Y));

请注意，我只渲染房子。我不在深度缓冲通道中渲染地板。

在此之后，我使用以下着色器对渲染代表地板的四边形：

/* [VERT] */ 
#version 330

in vec3 in_Position;
in vec2 in_TexCoord;

uniform mat4 shadowMatrix;
uniform mat4 mvp;

out vec2 UV;
out vec4 shadowProj;

void main()

    gl_Position = mvp*vec4(in_Position,1.0);
    shadowProj = shadowMatrix*vec4(in_Position,1.0);
    UV = in_TexCoord;

片段着色器：

/* [FRAG] */ 
#version 330

in vec2 UV;
in vec4 shadowProj;

out vec4 fragColor;

uniform sampler2D texturex;
uniform sampler2DShadow shadowMap;

void main()

    fragColor = vec4(texture(texturex, UV).rgb,1);

    float shadow = 1.0;
    shadow = textureProj(shadowMap,shadowProj);

    fragColor *= shadow;

然后我再次用颜色绘制房子和......地板：

textureShader.use();

glUniform1i(baseImageLoc, 0); //Texture unit 0 is for base images.
glUniform1i(shadowMapLoc, 1); //Texture unit 1 is for shadow maps.

glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, floorTexture);

glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, shadowTexture);
textureShader["shadowMatrix"] = projectionMatrix*pointLight.viewMatrix*floorMatrix;
textureShader["mvp"] = projectionMatrix*viewMatrix*floorMatrix;
CALL_GL(glBindVertexArray(floorVAO));
CALL_GL(glDrawArrays(GL_TRIANGLES,0,18));

glfwSwapBuffers();

以前有人见过这种行为吗？知道有什么问题吗？顺便说一句，灯光的坐标直接将它放在房子的顶部，所以阴影应该直接位于地板上的房子下方（但它最终会侧身）。

这里是我如何生成阴影 FBO 的参考：

int shadowMapWidth = WINDOW_SIZE_X * (int)SHADOW_MAP_RATIO;
int shadowMapHeight =  WINDOW_SIZE_Y * (int)SHADOW_MAP_RATIO;

glGenTextures(1, &shadowTexture);
glBindTexture(GL_TEXTURE_2D, shadowTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, shadowMapWidth, shadowMapHeight, 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_BYTE, 0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_COMPARE_REF_TO_TEXTURE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_FUNC, GL_LESS);
glTexImage2D(GL_TEXTURE_2D,0,GL_DEPTH_COMPONENT,shadowMapWidth,shadowMapHeight,0,GL_DEPTH_COMPONENT,GL_FLOAT,NULL);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_COMPARE_MODE,GL_COMPARE_R_TO_TEXTURE);
glBindTexture(GL_TEXTURE_2D, 0); //unbind the texture

glGenFramebuffers(1, &shadowFBO);
glBindFramebuffer(GL_FRAMEBUFFER, shadowFBO);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, shadowTexture, 0);
glDrawBuffer(GL_NONE);
glReadBuffer(GL_NONE);

if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
 printf("GL_FRAMEBUFFER_COMPLETE error 0x%x", glCheckFramebufferStatus(GL_FRAMEBUFFER)); 

glClearDepth(1.0f); glEnable(GL_DEPTH_TEST);
// Needed when rendering the shadow map. This will avoid artifacts.
glPolygonOffset(1.0f, 0.0f); glBindFramebuffer(GL_FRAMEBUFFER, 0);
//to convert the texture coordinates to -1 ~ 1
   GLfloat biasMatrixf[] = 
    0.5f, 0.0f, 0.0f, 0.0f,
    0.0f, 0.5f, 0.0f, 0.0f,
    0.0f, 0.0f, 0.5f, 0.0f,
    0.5f, 0.5f, 0.5f, 1.0f ;

biasMatrix = glm::make_mat4(biasMatrixf);

【参考方案1】：

您似乎忘记将阴影矩阵乘以偏置矩阵。

【讨论】：

谢谢！！！这就是问题所在！我的偏置矩阵也是错误的！ 0.5f 应该在底行，而不是最右边的列（我已经编辑了代码以反映这一点）。 GLfloat biasMatrixf[] = 0.5f, 0.0f, 0.0f, 0.0f, 0.0f, 0.5f, 0.0f, 0.0f, 0.0f, 0.0f, 0.5f, 0.0f, 0.5f, 0.5f, 0.5f , 1.0f ;

顺便说一句，干得好。你的小房子看起来很有趣:)。阴影映射是我的待办事项之一。实际上很害怕。