add particles lighting

src/graphics/render/MainBatch.cpp

@@ -3,6 +3,8 @@
 #include "graphics/core/Texture.hpp"
 #include "graphics/core/Mesh.hpp"
 #include "graphics/core/ImageData.hpp"
+#include "voxels/Chunks.hpp"
+#include "voxels/Chunk.hpp"
 
 static const vattr attrs[] = {
     {3}, {2}, {3}, {1}, {0}
@@ -62,3 +64,19 @@ void MainBatch::prepare(int vertices) {
         flush();
     }
 }
+
+glm::vec4 MainBatch::sampleLight(
+    const glm::vec3& pos, const Chunks& chunks, bool backlight
+) {
+    light_t light = chunks.getLight(
+        std::floor(pos.x), 
+        std::floor(std::min(CHUNK_H-1.0f, pos.y)), 
+        std::floor(pos.z));
+    light_t minIntensity = backlight ? 1 : 0;
+    return glm::vec4(
+        glm::max(Lightmap::extract(light, 0), minIntensity) / 15.0f,
+        glm::max(Lightmap::extract(light, 1), minIntensity) / 15.0f,
+        glm::max(Lightmap::extract(light, 2), minIntensity) / 15.0f,
+        glm::max(Lightmap::extract(light, 3), minIntensity) / 15.0f
+    );
+}