c++ - 为什么 SSAO 仅在特定角度/距离下起作用？

Question

我正在尝试复制 Sascha Willems SSAO example在使用 LearnOpenGL SSAO tutorial 时作为资源。但我的 SSAO 代码只是在某些角度/距离上部分覆盖了模型，并且在靠近物体时也有很强的自遮挡效果。

左边是我的渲染器，右边是Sascha Willems SSAO Example :

• 中心:Wrong | Correct
• 窗口:Wrong | Correct
• 楼梯:Wrong | Correct

编辑:RenderDoc 的正确图像上有一些奇怪的伪影。对此感到抱歉。

关于我的渲染器变量的一些说明:

• 位置+深度图像使用 VK_FORMAT_R32G32B32A32_SFLOAT 格式，在 RenderDoc 中看起来正确。 [ 1 ] [ 2 ]
• 普通图像使用 VK_FORMAT_R8G8B8A8_UNORM 格式，在 RenderDoc 中看起来正确。 [ 1 ]
• Position+Depth 和 Normal 图像使用带有 VK_SAMPLER_ADDRESS_MODE_CLAMP_TO_EDGE 的 VkSampler。
• SSAO 图像是 VK_FORMAT_R8_UNORM 并且正在由着色器正确写入。 [ 1 ]
• SSAO 噪声图像使用 VK_FORMAT_R32G32B32A32_SFLOAT 格式，在 RenderDoc 中看起来正确。 [ 1 ]
• SSAO 噪声图像使用带有 VK_SAMPLER_ADDRESS_MODE_REPEAT 的 VkSampler。

SSAO 噪声

// Random Generator
std::default_random_engine rndEngine(static_cast<unsigned>(glfwGetTime()));
std::uniform_real_distribution<float> rndDist(0.0f, 1.0f);

// SSAO random noise
std::vector<glm::vec4> ssaoNoise(SSAO_NOISE_DIM * SSAO_NOISE_DIM);
for (uint32_t i = 0; i < static_cast<uint32_t>(ssaoNoise.size()); i++)
{
    ssaoNoise[i] = glm::vec4(rndDist(rndEngine) * 2.0f - 1.0f, rndDist(rndEngine) * 2.0f - 1.0f, 0.0f, 0.0f);
}

SSAO 内核

// Function for SSAOKernel generation
float lerp(float a, float b, float f)
{
    return a + f * (b - a);
}

// SSAO sample kernel
std::vector<glm::vec4> ssaoKernel(SSAO_KERNEL_SIZE);
for (uint32_t i = 0; i < SSAO_KERNEL_SIZE; i++)
{
    glm::vec3 sample(rndDist(rndEngine) * 2.0 - 1.0, rndDist(rndEngine) * 2.0 - 1.0, rndDist(rndEngine));
    sample = glm::normalize(sample);
    sample *= rndDist(rndEngine);
    float scale = float(i) / float(SSAO_KERNEL_SIZE);
    scale = lerp(0.1f, 1.0f, scale * scale);
    ssaoKernel[i] = glm::vec4(sample * scale, 0.0f);
}

SSAO 内核 XY 值介于 -1.0 和 1.0 之间，Z 值介于 0.0 和 1.0 之间:

ssaoKernel XYZ[0]: X: -0.0428458 Y: 0.0578492 Z: 0.0569087
ssaoKernel XYZ[1]: X: 0.0191572 Y: 0.0442375 Z: 0.00108795
ssaoKernel XYZ[2]: X: 0.00155709 Y: 0.0287552 Z: 0.024916
ssaoKernel XYZ[3]: X: -0.0169349 Y: -0.0298343 Z: 0.0272303
ssaoKernel XYZ[4]: X: 0.0469432 Y: 0.0348599 Z: 0.0573885
(...)
ssaoKernel XYZ[31]: X: -0.104106 Y: -0.434528 Z: 0.321963

GLSL 着色器

model.vert

mat3 normalMatrix = transpose(inverse(mat3(ubo.view * ubo.model)));
outNormalViewSpace = normalMatrix * inNormal;
outPositionViewSpace = vec3(ubo.view * ubo.model * vec4(inPosition, 1.0));

模型.frag

// These are identical to the camera
float near = 0.1; 
float far  = 100.0; 
  
float LinearizeDepth(float depth) 
{
    float z = depth * 2.0 - 1.0;
    return (2.0 * near * far) / (far + near - z * (far - near));    
}

(...)

outNormalViewSpace = vec4(normalize(inNormalViewSpace) * 0.5 + 0.5, 1.0);
outPositionDepth = vec4(inPositionViewSpace, LinearizeDepth(gl_FragCoord.z));

全屏.vert

outUV = vec2((gl_VertexIndex << 1) & 2, gl_VertexIndex & 2);
gl_Position = vec4(outUV * 2.0f - 1.0f, 0.0f, 1.0f);

ssao.frag

#version 450

layout (location = 0) in vec2 inUV;

layout (constant_id = 1) const int SSAO_KERNEL_SIZE = 32;
layout (constant_id = 2) const float SSAO_RADIUS = 0.5;

layout (binding = 0) uniform sampler2D samplerPositionDepth;
layout (binding = 1) uniform sampler2D samplerNormal;
layout (binding = 2) uniform sampler2D samplerSSAONoise;

layout (binding = 3) uniform SSAOKernel
{
    vec4 samples[SSAO_KERNEL_SIZE];
} ssaoKernel;

layout( push_constant ) uniform UniformBufferObject {
    mat4 projection;
} ubo;

layout (location = 0) out float outSSAO;

void main() 
{
    //
    // SSAO Post Processing (Pre-Blur)
    //

    // Get a random vector using a noise lookup
    ivec2 texDim = textureSize(samplerPositionDepth, 0); 
    ivec2 noiseDim = textureSize(samplerSSAONoise, 0);
    const vec2 noiseUV = vec2(float(texDim.x) / float(noiseDim.x), float(texDim.y) / (noiseDim.y)) * inUV;   
    vec3 randomVec = texture(samplerSSAONoise, noiseUV).xyz * 2.0 - 1.0;

    // Get G-Buffer values
    vec3 fragPos = texture(samplerPositionDepth, inUV).rgb;
    vec3 normal = normalize(texture(samplerNormal, inUV).rgb * 2.0 - 1.0);

    // Create TBN matrix
    vec3 tangent = normalize(randomVec - normal * dot(randomVec, normal));
    vec3 bitangent = cross(tangent, normal);
    mat3 TBN = mat3(tangent, bitangent, normal);

    // Calculate occlusion value
    float occlusion = 0.0f;
    for(int i = 0; i < SSAO_KERNEL_SIZE; i++)
    {       
        vec3 samplePos = TBN * ssaoKernel.samples[i].xyz;
        samplePos = fragPos + samplePos * SSAO_RADIUS; 
        
        // project
        vec4 offset = vec4(samplePos, 1.0f);
        offset = ubo.projection * offset; 
        offset.xyz /= offset.w; 
        offset.xyz = offset.xyz * 0.5f + 0.5f;  
        
        float sampleDepth = -texture(samplerPositionDepth, offset.xy).w;

        // Range check
        float rangeCheck = smoothstep(0.0f, 1.0f, SSAO_RADIUS / abs(fragPos.z - sampleDepth));
        occlusion += (sampleDepth >= samplePos.z ? 1.0f : 0.0f) * rangeCheck;  
    }
    occlusion = 1.0 - (occlusion / float(SSAO_KERNEL_SIZE));
    
    outSSAO = occlusion;
}

一定是某处设置错误或计算不当，但我不能完全确定。如果缺少相关内容，请随时请求额外的代码片段。

非常感谢任何帮助，谢谢!

Answer 1

归功于 mlkn在评论中指出 LinearizeDepth 函数看起来不正确。他是对的，有一个额外的不必要的“* 2.0 - 1.0”步骤不属于。谢谢你! :)

这是原始的、不正确的 LinearizeDepth 函数:

float LinearizeDepth(float depth) 
{
    float z = depth * 2.0 - 1.0;
    return (2.0 * near * far) / (far + near - z * (far - near));    
}

通过删除第一行，并将其更改为:

float LinearizeDepth(float depth) 
{
    return (2.0 * near * far) / (far + near - depth * (far - near));    
}

我的输出立即变成了这个，这似乎是正确的: