为什么只有在正确的位置呈现第一个阴影？

问题描述：

我正在研究Java + LWJGL项目。目前我正在尝试实现方差阴影贴图，但只有我在着色器中采样的第一个阴影贴图出现在正确的位置。为什么只有在正确的位置呈现第一个阴影？

片段着色器：

#version 330 core 

in vec2 passTexCoords; 
in vec4[4] shadowCoords; 

//Fragment color 
out vec4 out_Color; 

uniform sampler2D modelTexture; 
uniform sampler2D[4] shadowMaps; 

#define SHADOW_BIAS 0.0005 

float linstep(float low, float high, float v) { 
    return clamp((v-low)/(high-low), 0.0, 1.0); 
} 

//compare ... The depth of the fragment in shadow map sapce 
float sampleVarianceShadowMap(in sampler2D shadowMap, in vec2 coords, in float compare) { 

    /* This is the Code that I want to use when I know what the problem was. 
    vec2 moments = texture(shadowMap, coords.xy).rg; 

    float p = step(compare, moments.x); 
    float variance = max(moments.y - moments.x * moments.x, 0.00002); 

    float d = compare - moments.x; 
    float pMax = linstep(0.2, 1.0, variance/(variance + d*d)); 

    return min(max(p, pMax), 1.0); 
    */ 

    //============================================================================HERE=========================================================================HERE==================== 
    //THE ERROR OCCURES HERE: 

    //This doesn't work: 
    float visibility = step(compare-SHADOW_BIAS, texture(shadowMap, coords.xy).r); 
    return visibility; 

    //The shadows on the ground move in a weird way when the camera moves. 

    //But this does: 
    return step(compare-SHADOW_BIAS, texture(shadowMap, coords.xy).r); 

    //With this code the shadows are at the correct place. 

    //===========================================================================HERE==========================================================================HERE===================== 
} 

//To create a smooth darkness falloff at the edge of the shadow map 
float calcShadowMapVisibilityFalloff(in vec2 coords, in float falloffStart, in float gradient) { 
    float distFromTexCenter = length(coords * vec2(2.0) - vec2(1.0)); 
    float falloff = (clamp(pow(distFromTexCenter, gradient), falloffStart, 1.0) - falloffStart) * (1/(1-falloffStart)); 

    if(falloff > 1.0 || falloff < 0.0) { 
     falloff = 0; 
    } 

    return 1-falloff; 
} 

void main(void){ 

    float shadowInvertedBrightness = 1.0; 
    for(int i = 0; i < shadowMaps.length(); i++) 
    { 
     float visibility = 1 - sampleVarianceShadowMap(shadowMaps[i], shadowCoords[i].xy, shadowCoords[i].z); 
     shadowInvertedBrightness -= (visibility/shadowMaps.length()) * calcShadowMapVisibilityFalloff(shadowCoords[i].xy, 0.85, 2.0); 
    } 

    shadowInvertedBrightness = clamp(shadowInvertedBrightness, 0.2, 1.0); 

    //.bgra because I save textures with the BGRA format (I've read its faster) 
    out_Color = texture(modelTexture, passTexCoords).bgra * vec4(shadowInvertedBrightness,shadowInvertedBrightness,shadowInvertedBrightness,1); 
}

顶点着色器：

#version 330 core 

//Vertex coords 
in vec3 position; 
//Texture coords 
in vec2 texCoords; 

//The MVP matrix of the entity 
uniform mat4 MVPMat; 
//The "To Shadow Map Space" matrix 
uniform mat4[4] shadowMVPBiasMats; 
//The Transformation matrix of the entity 
uniform mat4 transformMat; 

out vec2 passTexCoords; 
//Shadow map sample coords 
out vec4[4] shadowCoords; 

void main(void) { 
    gl_Position = MVPMat * vec4(position, 1.0); 

    vec4 worldPos = transformMat * vec4(position, 1.0); 

    for(int i = 0; i < shadowMVPBiasMats.length(); i++) { 
     shadowCoords[i] = shadowMVPBiasMats[i] * worldPos; 
    } 

    passTexCoords = texCoords; 
}

完整的代码（示例项目，你可以在Eclipse中导入）和截图：

Screenshots and source code（着色器文件在src/ShadowTest/rendering /，屏幕截图/）

系统信息：

操作系统：Windows主页，版本：10.0.15063
GPU：英特尔高清显卡520
GPU驱动程序版本：20.19.15.4642（通过Medion公司）

请提供更多信息。一些截图等。你看到人们低估了你。这是因为没有办法帮助你提供的数据。而且，GLSL是不够的。你的问题可以在客户端使用着色器输入。 –

我会建议一个一个地测试你的shadowMap，首先删除你的main，然后加上float visibility = 1;如果（shadowCoord [i] .z-SHADOW_BIAS> texture（shadowMap [i]，shadowCoord [i] .xy）.r）{visibility = 0; } out_Color = texture（modelTexture，passTexCoords）.bgra * vec4（visibility，visibility，visibility，1）;并告诉我们你看到的一个。您也可以尝试将影子地图保存在磁盘上并在查看器中显示它们 –

如果您需要更多代码或屏幕截图，请查看Google Drive链接。我也会尝试Draykoon D说的。 – Wendelin

答

这似乎是驱动程序中的一个错误，因为它在我使用NVIDIA GPU运行程序时不会发生。

的规避问题：

float textureShadowMap(in sampler2D shadowMap, in vec2 coords) { 
    return texture(shadowMap, coords).r; 
}

而在sampleVarianceShadowMap方法：

float visibility = step(compare-SHADOW_BIAS, textureShadowMap(shadowMap, coords)); 
return visibility;

因为我不是100％肯定，这是一个错误，它会如果有人可真好确认这一点。

为什么只有在正确的位置呈现第一个阴影？

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