【发布时间】：2014-08-06 03:10:05
【问题描述】：
在阅读了this tutorial 的基本光照后，我决定扩展着色器代码以处理任意数量的光照。根据我的谷歌搜索结果，推荐的方法是创建一个着色器存储缓冲区对象 (SSBO)，并在 Lamp 结构数组中创建一个缓冲区来表示灯光：
// all vec3 objects are from glm
struct Lamp {
vec3 pos;
float power;
vec3 color;
vec3 lightDirectionCameraSpace;
// this constructor is omitted in the struct definition in the shaders
Lamp(vec3 a, float b, vec3 c) {
pos = a;
power = b;
color = c;
}
};
// global variable
vector<Lamp> lights;
Lamp lmp1(vec3(0.0f, 0.0f, 10.0f), 40.0f, vec3(0.3f, 0.7f, 0.9f));
Lamp lmp2(vec3(0.0f, 0.0f, -10.0f), 40.0f, vec3(1.0f, 0.7f, 0.7f));
lights.push_back(lmp1);
lights.push_back(lmp2);
GLuint LightID;
glGenBuffers(1, &LightID);
然后，每个渲染通道，我将灯光缓冲到着色器中定义的 SSBO（见下文）：
glBindBuffer(GL_SHADER_STORAGE_BUFFER, LightID);
glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(Lamp)*lights.size(), &(lights[0]), GL_STATIC_DRAW);
// using binding 0 for the SSBO
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, LightID);
相关顶点着色器代码：
#version 430
...
struct Lamp {
vec3 pos;
float power;
vec3 color;
vec3 lightDirectionCameraSpace;
};
layout(std430, binding = 0) buffer LightArray {
Lamp[] lights;
} LightArr;
void main() {
...
for (int i = 0; i < LightArr.lights.length(); i++) {
// Vector that goes from the vertex to the light, in camera space. M is ommited because it's identity.
vec3 LightPosition_cameraspace = ( V * vec4(LightArr.lights[i].pos, 1)).xyz;
LightArr.lights[i].lightDirectionCameraSpace = LightPosition_cameraspace + EyeDirection_cameraspace;
}
...
相关片段着色器代码：
#version 430 core
...
// Ouput data
out vec3 glcolor;
struct Lamp {
vec3 pos;
float power;
vec3 color;
vec3 lightDirectionCameraSpace;
};
layout(std430, binding = 0) buffer LightArray {
Lamp[] lights;
} LightArr;
void main(){
// Material properties
vec3 MaterialDiffuseColor = texture2D( myTextureSampler, UV ).rgb;
vec3 MaterialAmbientColor = vec3(0.1,0.1,0.1) * MaterialDiffuseColor;
vec3 MaterialSpecularColor = vec3(0.3,0.3,0.3);
glcolor = vec3(0, 0, 0);
for (int i = 0; i < LightArr.lights.length(); i++) {
// Distance to the light
float distance = length( LightArr.lights[i].pos - Position_worldspace );
// Normal of the computed fragment, in camera space
vec3 n = normalize( Normal_cameraspace );
// Direction of the light (from the fragment to the light)
vec3 l = normalize( LightArr.lights[i].lightDirectionCameraSpace );
// Cosine of the angle between the normal and the light direction,
// clamped above 0
// - light is at the vertical of the triangle -> 1
// - light is perpendicular to the triangle -> 0
// - light is behind the triangle -> 0
float cosTheta = clamp( dot( n,l ), 0,1 );
// Eye vector (towards the camera)
vec3 E = normalize(EyeDirection_cameraspace);
// Direction in which the triangle reflects the light
vec3 R = reflect(-l,n);
// Cosine of the angle between the Eye vector and the Reflect vector,
// clamped to 0
// - Looking into the reflection -> 1
// - Looking elsewhere -> < 1
float cosAlpha = clamp( dot( E,R ), 0,1 );
glcolor +=
// Ambient : simulates indirect lighting
// MaterialAmbientColor +
// Diffuse : "color" of the object
MaterialDiffuseColor * LightArr.lights[i].color * LightArr.lights[i].power * cosTheta / (distance*distance) +
// Specular : reflective highlight, like a mirror
MaterialSpecularColor * LightArr.lights[i].color * LightArr.lights[i].power * pow(cosAlpha,5) / (distance*distance);
}
// compute total light, then add ambient
// Ambient : simulates indirect lighting
glcolor = MaterialAmbientColor + glcolor;
}
问题是当程序运行时，它只渲染添加到列表中的第一盏灯（这里是蓝色的）（但显示得非常正确）。我做了一些调试，发现不管我有多少灯，LightArr.lights.length() == 1。可能与此相关的是从宽法线角度照亮的表面上的一些闪烁，而当我只使用一盏灯时，这是不存在的。
编辑：我设法解决了这个问题，但我不知道为什么我的解决方案有效。我在vec3 color; 和vec3 lightDirectionCameraSpace; 之后将未使用的虚拟浮点变量（float foo; 和float bar;）添加到我的Lamp 结构（在着色器内部和外部）。现在，两盏灯都显示了，尽管在没有理由的情况下闪烁仍然存在。为什么添加垃圾变量会改变着色器渲染的灯光数量？
【问题讨论】：
标签： opengl visual-c++ shader