我想使用 OpenGL 和 GLSL 将定向光添加到我的场景中。问题在于,理论上正确的方法会产生错误的结果。
在顶点着色器中我执行以下操作:
光线的方向以世界坐标给出,并使用 viewMatrix 转换为相机坐标。使用法线矩阵将顶点的法线转换为相机坐标。
void main () {
vary_textureCoord = attribute_textureCoord;
vary_normal = mat3(normalMatrix) * attribute_normal;
vary_directionalLight_direction = viewMatrix * vec4(lightDir, 1.0);
gl_Position = projectionMatrix * viewMatrix * modelMatrix * vec4(attribute_position, 1.0);
}
因此两个向量都位于相机坐标中并传递给片段着色器。片段着色器使用光线的法线和方向来计算光线强度。
void main () {
vec3 normalizedNormal = normalize(vary_normal);
vec4 color = texture(tex, vary_textureCoord);
float directionalLightIntensity = max(0.0, dot(normalizedNormal, normalize(-vary_directionalLight_direction.xyz)));
out_color = color * directionalLightIntensity;
}
这个着色器导致的结果是光线不是静态的而是随着相机移动。使用此行更改顶点着色器:
vary_directionalLight_direction = transpose(inverse(viewMatrix)) * vec4(lightDir, 1.0);
得到了想要的结果。
那么我到底做错了什么或者哪里有误解呢?
这里是完整的着色器代码:
顶点着色器:
# version 330
layout(location = 0) in vec3 attribute_position;
layout(location = 2) in vec2 attribute_textureCoord;
layout(location = 3) in vec3 attribute_normal;
uniform mat4 projectionMatrix;
uniform mat4 viewMatrix;
uniform mat4 modelMatrix;
uniform mat4 normalMatrix;
uniform vec3 lightDir;
out vec2 vary_textureCoord;
out vec3 vary_normal;
out vec4 vary_directionalLight_direction;
void main () {
vary_textureCoord = attribute_textureCoord;
vary_normal = mat3(normalMatrix) * attribute_normal;
vary_directionalLight_direction = viewMatrix * vec4(lightDir, 1.0);
gl_Position = projectionMatrix * viewMatrix * modelMatrix * vec4(attribute_position, 1.0);
}
片段着色器:
# version 330
in vec2 vary_textureCoord;
in vec3 vary_normal;
in vec4 vary_directionalLight_direction;
uniform sampler2D tex;
out vec4 out_color;
void main () {
vec3 normalizedNormal = normalize(vary_normal);
vec4 color = texture(tex, vary_textureCoord);
float directionalLightIntensity = max(0.0, dot(normalizedNormal, normalize(-vary_directionalLight_direction.xyz)));
out_color = color * directionalLightIntensity;
}