使用Subroutine在shader中封裝不同的函數，在CPU端選擇調用那個函數

效果如下圖所示

左側：環境光

中間：環境光 + 漫反射

右側：環境光 + 漫反射 + 高光

1、Subroutine 在shader中的內容

subroutine vec4 SurfaceColor();
subroutine uniform SurfaceColor U_SurfaceColor;

定義SurfaceColor()函數類型

環境光函數

// Ambient
subroutine (SurfaceColor) vec4 Ambient()
{
        // Ambient
        vec4 M_AmbientLightColor = vec4(0.2, 0.2, 0.2, 1.0);
        vec4 M_AmbientMaterial = vec4(0.2, 0.2, 0.2, 1.0);
        vec4 ambientColor = M_AmbientLightColor * M_AmbientMaterial;

        return ambientColor;
}

環境光+漫反射函數

subroutine (SurfaceColor) vec4 Diffuse()
{
        // Ambient
        vec4 M_AmbientLightColor = vec4(0.2, 0.2, 0.2, 1.0);
        vec4 M_AmbientMaterial = vec4(0.2, 0.2, 0.2, 1.0);
        vec4 ambientColor = M_AmbientLightColor * M_AmbientMaterial;

        // Diffuse
        vec3 M_LightPos = vec3(10.0, 10.0, 0.0);
        vec3 LightNormal = normalize(M_LightPos);       // 指向光源的單位向量
        vec3 NormalNormal = normalize(M_normal);      //  法線的單位向量

        // 點乘獲取光照強度
        vec4 M_DiffuseLightColor = vec4(1.0, 1.0, 1.0, 1.0);
        vec4 M_DiffuseMaterial = vec4(0.8, 0.8, 0.8, 1.0);
        vec4 diffuseColor = M_DiffuseLightColor * M_DiffuseMaterial * max(0.0, dot(NormalNormal, LightNormal));

        return ambientColor + texture2D(U_MainTexture, M_coord) * diffuseColor;
}

鏡面反射函數

subroutine (SurfaceColor) vec4 Specular()
{
        // Ambient
        vec4 M_AmbientLightColor = vec4(0.2, 0.2, 0.2, 1.0);
        vec4 M_AmbientMaterial = vec4(0.2, 0.2, 0.2, 1.0);
        vec4 ambientColor = M_AmbientLightColor * M_AmbientMaterial;

        // Diffuse
        vec3 M_LightPos = vec3(10.0, 10.0, 0.0);
        vec3 LightNormal = normalize(M_LightPos);       // 指向光源的單位向量
        vec3 NormalNormal = normalize(M_normal);      //  法線的單位向量

        // 點乘獲取光照強度
        vec4 M_DiffuseLightColor = vec4(1.0, 1.0, 1.0, 1.0);
        vec4 M_DiffuseMaterial = vec4(0.8, 0.8, 0.8, 1.0);
        vec4 diffuseColor = M_DiffuseLightColor * M_DiffuseMaterial * max(0.0, dot(NormalNormal, LightNormal));

        // 鏡面反射
        vec4 specularLightColor = vec4(1.0, 1.0, 1.0, 1.0);
        vec4 specularMaterial = vec4(0.4, 0.4, 0.4, 1.0);
        vec3 reflerDir = normalize(reflect(-LightNormal, NormalNormal));
        vec3 eyeDir = normalize(vec3(0.0) - M_WordPos.xyz);
        vec4 specularColor = specularLightColor * specularMaterial * pow(max(0.0, dot(reflerDir, eyeDir)), 180);

        return ambientColor + texture2D(U_MainTexture, M_coord) * diffuseColor + specularColor;
}

main函數

void main()
{
        gl_FragColor = U_SurfaceColor();
}

2、CPU端設置調用subrountine

獲取subrountine的Location

m_SubRoutineLocation = OpenGLCore->glGetSubroutineUniformLocation(programId,                        GL_FRAGMENT_SHADER, "U_SurfaceColor");
// 獲取 SubRoutine Index
m_AmbientIndex=OpenGLCore->glGetSubroutineIndex(programId,GL_FRAGMENT_SHADER,"Ambient");
m_DiffuseIndex=OpenGLCore->glGetSubroutineIndex(programId,GL_FRAGMENT_SHADER,"Diffuse");
m_SpecularIndex=OpenGLCore->glGetSubroutineIndex(programId,GL_FRAGMENT_SHADER,"Specular");

為U_SurfaceColor設置值

OpenGLCore->glUniformSubroutinesuiv(GL_FRAGMENT_SHADER, 1, &m_AmbientIndex);
OpenGLCore->glUniformSubroutinesuiv(GL_FRAGMENT_SHADER, 1, &m_DiffuseIndex);
OpenGLCore->glUniformSubroutinesuiv(GL_FRAGMENT_SHADER, 1, &m_SpecularIndex);

本文出自 “不會飛的紙飛機” 博客，請務必保留此出處http://douzhq.blog.51cto.com/12552184/1931020

基於Qt的OpenGL可編程管線學習（4）- 使用Subroutine繪制不同光照的模型