【发布时间】：2017-03-27 19:02:34
【问题描述】：
我正在尝试在片段着色器中实现 Oren-Nayar 光照，如 here 所示。
但是，我在地形上得到了一些奇怪的光照效果，如下所示。
我目前正在向着色器发送“视图方向”统一作为相机的“前”向量。我不确定这是否正确，因为移动相机会改变伪影。
将“前”向量乘以 MVP 矩阵会得到更好的结果，但从某些角度查看地形时，伪影仍然非常明显。在黑暗区域和屏幕边缘周围尤其明显。
什么可能导致这种效果？
工件示例
场景的外观
顶点着色器
#version 450
layout(location = 0) in vec3 position;
layout(location = 1) in vec3 normal;
out VS_OUT {
vec3 normal;
} vert_out;
void main() {
vert_out.normal = normal;
gl_Position = vec4(position, 1.0);
}
镶嵌控制着色器
#version 450
layout(vertices = 3) out;
in VS_OUT {
vec3 normal;
} tesc_in[];
out TESC_OUT {
vec3 normal;
} tesc_out[];
void main() {
if(gl_InvocationID == 0) {
gl_TessLevelInner[0] = 1.0;
gl_TessLevelInner[1] = 1.0;
gl_TessLevelOuter[0] = 1.0;
gl_TessLevelOuter[1] = 1.0;
gl_TessLevelOuter[2] = 1.0;
gl_TessLevelOuter[3] = 1.0;
}
tesc_out[gl_InvocationID].normal = tesc_in[gl_InvocationID].normal;
gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;
}
镶嵌评估着色器
#version 450
layout(triangles, equal_spacing) in;
in TESC_OUT {
vec3 normal;
} tesc_in[];
out TESE_OUT {
vec3 normal;
float height;
vec4 shadow_position;
} tesc_out;
uniform mat4 model_view;
uniform mat4 model_view_perspective;
uniform mat3 normal_matrix;
uniform mat4 depth_matrix;
vec3 lerp(vec3 v0, vec3 v1, vec3 v2) {
return (
(vec3(gl_TessCoord.x) * v0) +
(vec3(gl_TessCoord.y) * v1) +
(vec3(gl_TessCoord.z) * v2)
);
}
vec4 lerp(vec4 v0, vec4 v1, vec4 v2) {
return (
(vec4(gl_TessCoord.x) * v0) +
(vec4(gl_TessCoord.y) * v1) +
(vec4(gl_TessCoord.z) * v2)
);
}
void main() {
gl_Position = lerp(
gl_in[0].gl_Position,
gl_in[1].gl_Position,
gl_in[2].gl_Position
);
tesc_out.normal = normal_matrix * lerp(
tesc_in[0].normal,
tesc_in[1].normal,
tesc_in[2].normal
);
tesc_out.height = gl_Position.y;
tesc_out.shadow_position = depth_matrix * gl_Position;
gl_Position = model_view_perspective * gl_Position;
}
片段着色器
#version 450
in TESE_OUT {
vec3 normal;
float height;
vec4 shadow_position;
} frag_in;
out vec4 colour;
uniform vec3 view_direction;
uniform vec3 light_position;
#define PI 3.141592653589793
void main() {
const vec3 ambient = vec3(0.1, 0.1, 0.1);
const float roughness = 0.8;
const vec4 water = vec4(0.0, 0.0, 0.8, 1.0);
const vec4 sand = vec4(0.93, 0.87, 0.51, 1.0);
const vec4 grass = vec4(0.0, 0.8, 0.0, 1.0);
const vec4 ground = vec4(0.49, 0.27, 0.08, 1.0);
const vec4 snow = vec4(0.9, 0.9, 0.9, 1.0);
if(frag_in.height == 0.0) {
colour = water;
} else if(frag_in.height < 0.2) {
colour = sand;
} else if(frag_in.height < 0.575) {
colour = grass;
} else if(frag_in.height < 0.8) {
colour = ground;
} else {
colour = snow;
}
vec3 normal = normalize(frag_in.normal);
vec3 view_dir = normalize(view_direction);
vec3 light_dir = normalize(light_position);
float NdotL = dot(normal, light_dir);
float NdotV = dot(normal, view_dir);
float angleVN = acos(NdotV);
float angleLN = acos(NdotL);
float alpha = max(angleVN, angleLN);
float beta = min(angleVN, angleLN);
float gamma = dot(view_dir - normal * dot(view_dir, normal), light_dir - normal * dot(light_dir, normal));
float roughnessSquared = roughness * roughness;
float roughnessSquared9 = (roughnessSquared / (roughnessSquared + 0.09));
// calculate C1, C2 and C3
float C1 = 1.0 - 0.5 * (roughnessSquared / (roughnessSquared + 0.33));
float C2 = 0.45 * roughnessSquared9;
if(gamma >= 0.0) {
C2 *= sin(alpha);
} else {
C2 *= (sin(alpha) - pow((2.0 * beta) / PI, 3.0));
}
float powValue = (4.0 * alpha * beta) / (PI * PI);
float C3 = 0.125 * roughnessSquared9 * powValue * powValue;
// now calculate both main parts of the formula
float A = gamma * C2 * tan(beta);
float B = (1.0 - abs(gamma)) * C3 * tan((alpha + beta) / 2.0);
// put it all together
float L1 = max(0.0, NdotL) * (C1 + A + B);
// also calculate interreflection
float twoBetaPi = 2.0 * beta / PI;
float L2 = 0.17 * max(0.0, NdotL) * (roughnessSquared / (roughnessSquared + 0.13)) * (1.0 - gamma * twoBetaPi * twoBetaPi);
colour = vec4(colour.xyz * (L1 + L2), 1.0);
}
【问题讨论】：
-
如果 Oren-Nayar 的成本太高，您可以考虑使用wrap lighting。