optimize Skybox

src/graphics/render/Skybox.cpp

@@ -138,6 +138,7 @@ void Skybox::draw(
 }
 
 void Skybox::refresh(const DrawContext& pctx, float t, float mie, uint quality) {
+    frameid++;
     float dayTime = t;
     DrawContext ctx = pctx.sub();
     ctx.setDepthMask(false);
@@ -152,7 +153,31 @@ void Skybox::refresh(const DrawContext& pctx, float t, float mie, uint quality)
     glActiveTexture(GL_TEXTURE1);
     cubemap->bind();
     shader->use();
+    t *= M_PI*2.0f;
+    
+    lightDir = glm::normalize(glm::vec3(sin(t), -cos(t), 0.0f));
+    shader->uniform1i("u_quality", quality);
+    shader->uniform1f("u_mie", mie);
+    shader->uniform1f("u_fog", mie - 1.0f);
+    shader->uniform3f("u_lightDir", lightDir);
+    shader->uniform1f("u_dayTime", dayTime);
 
+    if (glm::abs(mie-prevMie) + glm::abs(t-prevT) >= 0.01) {
+        for (uint face = 0; face < 6; face++) {
+            refreshFace(face, cubemap);
+        }
+    } else {
+        uint face = frameid % 6;
+        refreshFace(face, cubemap);
+    }
+    prevMie = mie;
+    prevT = t;
+    
+    cubemap->unbind();
+    glActiveTexture(GL_TEXTURE0);
+}
+
+void Skybox::refreshFace(uint face, Cubemap* cubemap) {
     const glm::vec3 xaxs[] = {
         {0.0f, 0.0f, -1.0f},
         {0.0f, 0.0f, 1.0f},
@@ -181,23 +206,11 @@ void Skybox::refresh(const DrawContext& pctx, float t, float mie, uint quality)
         {0.0f, 0.0f, -1.0f},
         {0.0f, 0.0f, 1.0f},
     };
-    t *= M_PI*2.0f;
-    
-    lightDir = glm::normalize(glm::vec3(sin(t), -cos(t), 0.0f));
-    shader->uniform1i("u_quality", quality);
-    shader->uniform1f("u_mie", mie);
-    shader->uniform1f("u_fog", mie - 1.0f);
-    shader->uniform3f("u_lightDir", lightDir);
-    shader->uniform1f("u_dayTime", dayTime);
-    for (uint face = 0; face < 6; face++) {
-        glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_CUBE_MAP_POSITIVE_X + face, cubemap->getId(), 0);
-        shader->uniform3f("u_xaxis", xaxs[face]);
-        shader->uniform3f("u_yaxis", yaxs[face]);
-        shader->uniform3f("u_zaxis", zaxs[face]);
-        mesh->draw();
-    }
-    cubemap->unbind();
-    glActiveTexture(GL_TEXTURE0);
+    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_CUBE_MAP_POSITIVE_X + face, cubemap->getId(), 0);
+    shader->uniform3f("u_xaxis", xaxs[face]);
+    shader->uniform3f("u_yaxis", yaxs[face]);
+    shader->uniform3f("u_zaxis", zaxs[face]);
+    mesh->draw();
 }
 
 void Skybox::bind() const {

src/graphics/render/Skybox.hpp

@@ -12,6 +12,8 @@ class Shader;
 class Assets;
 class Camera;
 class Batch3D;
+class Shader;
+class Cubemap;
 class Framebuffer;
 class DrawContext;
 
@@ -33,11 +35,16 @@ class Skybox {
     std::unique_ptr<Mesh> mesh;
     std::unique_ptr<Batch3D> batch3d;
     std::vector<skysprite> sprites;
+    int frameid = 0;
+
+    float prevMie = -1.0f;
+    float prevT = -1.0f;
 
     void drawStars(float angle, float opacity);
     void drawBackground(
         const Camera& camera, const Assets& assets, int width, int height
     );
+    void refreshFace(uint face, Cubemap* cubemap);
 public:
     Skybox(uint size, Shader* shader);
     ~Skybox();