Phong 着色和 Gouraud 着色有什么区别? [英] What is the difference between Phong Shading and Gouraud Shading?
问题描述
据我所知，Gouraud shading 计算每个顶点的光色并对该颜色进行插值，而 Phong shading 为每个像素插值法线并计算光色基于该插值.
然而，当我试图用数学方法推导出光色时，我最终得到了两种方法相同的公式！
(其中n1和n2为两个顶点的法线，t为插值系数，Lem>是光的方向，上面的平面和虚线表示屏幕和一个像素.)
两种方法的光色推导如下:
Gouraud:
L = t*dot(n1,L) + (1-t)*dot(n2,L)Phong:
L = dot(t*n1+(1-t)*n2,L)
结果是一样的.
谁能告诉我我的推导有什么问题?
虽然在
另见:
GLSL 固定函数片段程序替换
Phong 和 Gouraud 阴影
Gouraud 着色/Phong 着色
As I understand it, Gouraud shading calculates light color for each vertex and does interpolation on that color, whereas Phong shading interpolates the normal for each pixel and calculates light color based on that interpolated value.
However, when I tried to derive the light color mathematically, I ended up with the same formula for both ways!
(Where n1 and n2 are the normals of the two vertices, t is the coefficient for interpolation, L is the light direction, and the plane on the top and the dotted line means screen and a pixel.)
The light colors for the two methods are derived as:
Gouraud:
L = t*dot(n1,L) + (1-t)*dot(n2,L)Phong:
L = dot(t*n1+(1-t)*n2,L)
and the results are the same.
Can anyone tell me what's wrong with my derivations?
While at Gouraud shading the light is calculates per vertex (Vertex shader), at Phong shading the light is calculates per fragment (fragment shader).
Therefore, Gouraud shading calculates the light for the vertices (corners) of a primitive and interpolates the light for the fragments covered by the primitive.
With Phong shading, the light is calculated separately for each fragment.
In general a light is computed by the Bidirectional reflectance distribution function. The function computes the reflectance of the light on a surface and depends on the vector of the incident light, the point of view and the normal vector of the surface.
At Gouraud shading the vertex color (reflectance) is interpolated and at Phong shading the 3 vectors are interpolated. That won't make any difference if the function c = brdf(l, v, n) is linear, where c is the color, l is the light direction, v is the view vector and n is the normal vector (e.g. Lambertian reflectance). But if the light model is not linear (e.g. Blinn–Phong), then the linear interpolation of Gouraud shading leads to different results.
Compare Gouraud shading and Phong shading
See also:
GLSL fixed function fragment program replacement
Phong and Gouraud Shading
Gouraud shading / Phong shading
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