opengl es 2.0 -优化片段着色器

Question

我正在为Android/iOS开发一个游戏，需要优化渲染。该游戏使用户能够变形地形，所以我使用一个灰度图像的地形(值1在地形意味着坚实的地面，0表示没有地面)，并应用碎片阴影(也有一个背景图像)。这与60 fps常数很好，但问题是，我还需要渲染一个边界的地形边缘。为此，我在变形时模糊边缘，在碎片着色器中，我根据地形密度/透明度绘制边框(边框为1x64纹理)。

问题是，当渲染边框时，我需要做一个动态纹理读取，将帧速率降到20。有什么方法可以优化这个吗？如果我用一个统一的浮点数组来替换边框纹理，它会有帮助吗?还是和从2d纹理中读取一样？

着色器代码：

 varying mediump vec2 frag_background_texcoord;
 varying mediump vec2 frag_density_texcoord;
 varying mediump vec2 frag_terrain_texcoord;

 uniform sampler2D density_texture;
 uniform sampler2D terrain_texture;
 uniform sampler2D mix_texture;
 uniform sampler2D background_texture;

 void main()
 {
    lowp vec4 background_color = texture2D(background_texture, frag_background_texcoord);
    lowp vec4 terrain_color = texture2D(terrain_texture, frag_terrain_texcoord);

    highp float density = texture2D(density_texture, frag_density_texcoord).a;

    if(density > 0.5)
    {
         lowp vec4 mix_color = texture2D(mix_texture, vec2(density, 1.0)); <- dynamic texture read (FPS drops to 20), would replacing this with a uniform float array help (would also need to calculate the index in the array)?
         gl_FragColor = mix(terrain_color, mix_color, mix_color.a);
    } else
    {
         gl_FragColor =  background_color;
    }
 }

Answer 1

弄明白了。我修的方法是移除所有的分支。现在运行到60 now。优化的代码：

varying mediump vec2 frag_background_texcoord;
varying mediump vec2 frag_density_texcoord;
varying mediump vec2 frag_terrain_texcoord;

uniform sampler2D density_texture;   
uniform sampler2D terrain_texture;
uniform sampler2D mix_texture;
uniform sampler2D background_texture;

void main()
{
   lowp vec4 background_color = texture2D(background_texture, frag_background_texcoord);
   lowp vec4 terrain_color = texture2D(terrain_texture, frag_terrain_texcoord);

   lowp vec4 mix_color = texture2D(mix_texture, vec2(density, 0.0));
   lowp float density = texture2D(density_texture, frag_density_texcoord).a;

   gl_FragColor = mix(mix(bg_color, terrain_color, mix_color.r), mix_color, mix_color.a);       
}