SSAO 阴影随着相机移动奇怪（计算 gbuffer 错误）

Posted 2023-02-22

【中文标题】SSAO 阴影随着相机移动奇怪（计算 gbuffer 错误）

【英文标题】：SSAO shading moves weird with camera (calculating gbuffer wrong)

【发布时间】：2016-10-11 03:59:41

【问题描述】：

我正在尝试通过本教程实现这个版本的 ssao：

http://www.learnopengl.com/#!Advanced-Lighting/SSAO

这是我最终的渲染纹理。

当我移动相机时，阴影似乎会跟随

好像我错过了某种与相机的矩阵乘法。

代码

gBuffer 顶点

#version 330 core
layout (location = 0) in vec3 vertexPosition;
layout (location = 1) in vec3 vertexNormal;

out vec3 position;
out vec3 normal;

uniform mat4 m;
uniform mat4 v;
uniform mat4 p;
uniform mat4 n;

void main()

    vec4 viewPos = v * m * vec4(vertexPosition, 1.0f);
    position = viewPos.xyz;
    gl_Position = p * viewPos;
    normal = vec3(n * vec4(vertexNormal, 0.0f));

gBuffer 片段

#version 330 core
layout (location = 0) out vec4 gPosition;
layout (location = 1) out vec3 gNormal;
layout (location = 2) out vec4 gColor;

in vec3 position;
in vec3 normal;

const float NEAR = 0.1f;
const float FAR = 50.0f;
float LinearizeDepth(float depth)

    float z = depth * 2.0f - 1.0f;
    return (2.0 * NEAR * FAR) / (FAR + NEAR - z * (FAR - NEAR));


void main()
   
    gPosition.xyz = position;
    gPosition.a = LinearizeDepth(gl_FragCoord.z);
    gNormal = normalize(normal);
    gColor.rgb = vec3(1.0f);

SSAO 顶点

#version 330 core

layout (location = 0) in vec3 vertexPosition;
layout (location = 1) in vec2 texCoords;

out vec2 UV;

void main()
    gl_Position =  vec4(vertexPosition, 1.0f);
    UV = texCoords;

SSAO 片段

#version 330 core

out float FragColor;
in vec2 UV;

uniform sampler2D gPositionDepth;
uniform sampler2D gNormal;
uniform sampler2D texNoise;
uniform vec3 samples[32];
uniform mat4 projection;

// parameters (you'd probably want to use them as uniforms to more easily tweak the effect)
int kernelSize = 32;
float radius = 1.0;

// tile noise texture over screen based on screen dimensions divided by noise size
const vec2 noiseScale = vec2(1024.0f/4.0f, 1024.0f/4.0f);

void main()

    // Get input for SSAO algorithm
    vec3 fragPos = texture(gPositionDepth, UV).xyz;
    vec3 normal = texture(gNormal, UV).rgb;
    vec3 randomVec = texture(texNoise, UV * noiseScale).xyz;
    // Create TBN change-of-basis matrix: from tangent-space to view-space
    vec3 tangent = normalize(randomVec - normal * dot(randomVec, normal));
    vec3 bitangent = cross(normal, tangent);
    mat3 TBN = mat3(tangent, bitangent, normal);
    // Iterate over the sample kernel and calculate occlusion factor
    float occlusion = 0.0;
    for(int i = 0; i < kernelSize; ++i)
    
        // get sample position
        vec3 sample = TBN * samples[i]; // From tangent to view-space
        sample = fragPos + sample * radius;

        // project sample position (to sample texture) (to get position on screen/texture)
        vec4 offset = vec4(sample, 1.0);
        offset = projection * offset; // from view to clip-space
        offset.xyz /= offset.w; // perspective divide
        offset.xyz = offset.xyz * 0.5 + 0.5; // transform to range 0.0 - 1.0

       // get sample depth
        float sampleDepth = -texture(gPositionDepth, offset.xy).w; // Get depth value of kernel sample

        // range check & accumulate
        float rangeCheck = smoothstep(0.0, 1.0, radius / abs(fragPos.z - sampleDepth ));
        occlusion += (sampleDepth >= sample.z ? 1.0 : 0.0) * rangeCheck;
    
    occlusion = 1.0 - (occlusion / kernelSize);
    FragColor = occlusion;

我已经阅读并看到有人有类似的问题，并将视图矩阵传递到 ssao 着色器并乘以 sampleDepth：

float sampleDepth = (viewMatrix * -texture(gPositionDepth, offset.xy)).w;

但这似乎只会让事情变得更糟。

这是另一个俯视图，您可以看到阴影随着相机移动

如果我以某种方式定位我的相机，事情就会对齐

【参考方案1】：

虽然我只能在 gBuffer 顶点着色器中假设您的法线矩阵 n 的值，但您似乎没有将法线存储在视图空间中，而是存储在世界空间中。由于 SSAO 计算是在屏幕空间中完成的，这可以（至少部分）解释意外行为。在这种情况下，您需要将视图矩阵 v 与法线相乘，然后再将它们存储到 gBuffer（可能更有效，但可能会干扰您的其他着色计算）或在检索它们之后。

【讨论】：

我的正常矩阵是 glm::mat4 n = glm::transpose(glm::inverse(view * model));所以我会在顶点着色器中相乘 normal = vec3(v * n * vec4(vertexNormal, 0.0f)); ?如何将其反转为照明？

另外，你有我的正常缓冲区应该是什么样子的例子吗？当我在网上搜索gbuffer延迟渲染和ssao时，有时正常的buffer有不同的颜色

我没有例子，但你的正常矩阵应该是glm::mat4 n = view * glm::transpose(glm::inverse(model))。您不应该转置和反转视图矩阵。