原文 http://www.cnblogs.com/CGDeveloper/archive/2008/07/02/1233816.html
众所周知，OpenGL固定管线只提供了最多8盏灯光。如何使得自己的场景之中拥有更多的灯光效果呢？
这里提供一种使用GLSL shader实现更多数量的局部光照。
在GLSL里，首先建立光照参数数据结构：
struct myLightParams
{
bool enabled;
vec4 position;
vec4 ambient;
vec4 diffuse;
vec4 specular;
vec3 spotDirection;
float spotCutoff;
float spotExponent;
float constantAttenuation;
float linearAttenuation;
float quadraticAttenuation;
};
然后，需要app传入的参数：
const int maxLightCount = 32;
uniform myLightParams light[maxLightCount];
uniform bool bLocalViewer;
uniform bool bSeperateSpecualr;
主函数：
void main()
{
gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
vec4 pos = gl_ModelViewMatrix * gl_Vertex;
vec3 epos = vec3(pos)/pos.w;
vec3 normal = normalize(gl_NormalMatrix * gl_Normal);
vec3 eye;
if (bLocalViewer)
eye = -normalize(epos);
else
eye = vec3(0, 0, 1.0);
vec4 amb = vec4(0);
vec4 diff = vec4(0);
vec4 spec = vec4(0);
for (int i=0; i<maxLightCount; i++)
{
if (light[i].enabled == false)
continue;
if (light[i].position.w == 0)
{
DirectionalLight(i, eye, epos, normal, amb, diff, spec);
}
else if (light[i].spotCutoff == 180.0)
{
PointLight(i, eye, epos, normal, amb, diff, spec);
}
else
{
SpotLight(i, eye, epos, normal, amb, diff, spec);
}
}
vec4 color = gl_FrontLightModelProduct.sceneColor +
amb * gl_FrontMaterial.ambient +
diff * gl_FrontMaterial.diffuse;
if (bSeperateSpecualr)
{
gl_FrontSecondaryColor = spec * gl_FrontMaterial.specular;
}
else
{
gl_FrontSecondaryColor = vec4(0, 0, 0, 1.0);
color += spec * gl_FrontMaterial.specular;
}
gl_FrontColor = color;
}
对于方向光源的计算：
void DirectionalLight(int i, vec3 eye, vec3 epos, vec3 normal,
inout vec4 amb, inout vec4 diff, inout vec4 spec)
{
float dotVP = max(0, dot(normal, normalize(vec3(light[i].position))));
float dotHV = max(0, dot(normal, normalize(eye+normalize(vec3(light[i].position)))));
amb += light[i].ambient;
diff += light[i].diffuse * dotVP;
spec += light[i].specular * pow(dotHV, gl_FrontMaterial.shininess);
}
对于点光源：
void PointLight(int i, vec3 eye, vec3 epos, vec3 normal,
inout vec4 amb, inout vec4 diff, inout vec4 spec)
{
vec3 VP = vec3(light[i].position) - epos;
float d = length(VP);
VP = normalize(VP);
float att = 1.0/(light[i].constantAttenuation + light[i].linearAttenuation*d + light[i].quadraticAttenuation*d*d);
vec3 h = normalize(VP+eye);
float dotVP = max(0, dot(normal, VP));
float dotHV = max(0, dot(normal, h));
amb += light[i].ambient * att;
diff += light[i].diffuse * dotVP * att;
spec += light[i].specular * pow(dotHV, gl_FrontMaterial.shininess) * att;
}
对于聚光灯：
void SpotLight(int i, vec3 eye, vec3 epos, vec3 normal,
inout vec4 amb, inout vec4 diff, inout vec4 spec)
{
vec3 VP = vec3(light[i].position) - epos;
float d = length(VP);
VP = normalize(VP);
float att = 1.0/(light[i].constantAttenuation + light[i].linearAttenuation*d + light[i].quadraticAttenuation*d*d);
float dotSpot = dot(-VP, normalize(light[i].spotDirection));
float cosCutoff = cos(light[i].spotCutoff*3.1415926/180.0);
float spotAtt = 0;
if (dotSpot < cosCutoff)
spotAtt = 0;
else
spotAtt = pow(dotSpot, light[i].spotExponent);
att *= spotAtt;
vec3 h = normalize(VP+eye);
float dotVP = max(0, dot(normal, VP));
float dotHV = max(0, dot(normal, h));
amb += light[i].ambient * att;
diff += light[i].diffuse * dotVP * att;
spec += light[i].specular * pow(dotHV, gl_FrontMaterial.shininess) * att;
}
这样，对于场景之中的任意对象，它所能够接受计算的光源就可以突破8个的限制了。
上述光照计算是遵循OpenGL spec的，因此与固定管线的效果是一致的。