Fix StarVBOw NullPointerException in renderSky (#11)

generateStars() was calling tessellator.draw() instead of creating a
VertexBuffer, leaving starVBO nuull and crashing on bindBuffer()

Author: s12kuma01

src/main/java/jp/s12kuma01/celeritasextra/client/RenderStars.java

@@ -1,8 +1,6 @@
 package jp.s12kuma01.celeritasextra.client;
 
 import net.minecraft.client.renderer.BufferBuilder;
-import net.minecraft.client.renderer.Tessellator;
-import net.minecraft.client.renderer.vertex.DefaultVertexFormats;
 
 import java.util.Random;
 
@@ -14,17 +12,17 @@
 public class RenderStars {
 
     /**
-     * Generate star vertex data into the tessellator.
+     * Generate star vertex data into an already-begun BufferBuilder.
      * Called from the mixin that overrides RenderGlobal.generateStars().
      * Uses the same seed (10842L) and algorithm as vanilla for deterministic rendering.
+     *
+     * @param buffer     a BufferBuilder that has already had begin() called
+     * @param totalStars number of stars to generate
      */
-    public static void generateStars(int totalStars) {
+    public static void generateStars(BufferBuilder buffer, int totalStars) {
         if (totalStars <= 0) return;
 
         Random random = new Random(10842L);
-        Tessellator tessellator = Tessellator.getInstance();
-        BufferBuilder buffer = tessellator.getBuffer();
-        buffer.begin(7, DefaultVertexFormats.POSITION);
 
         for (int i = 0; i < totalStars; ++i) {
             double x = random.nextFloat() * 2.0F - 1.0F;
@@ -69,6 +67,5 @@ public static void generateStars(int totalStars) {
             }
         }
 
-        tessellator.draw();
     }
 }

src/main/java/jp/s12kuma01/celeritasextra/mixin/render/sky/MixinRenderGlobalStars.java

@@ -4,11 +4,16 @@
 import com.llamalad7.mixinextras.injector.wrapoperation.WrapOperation;
 import jp.s12kuma01.celeritasextra.client.CeleritasExtraClientMod;
 import jp.s12kuma01.celeritasextra.client.RenderStars;
+import net.minecraft.client.renderer.BufferBuilder;
 import net.minecraft.client.renderer.RenderGlobal;
+import net.minecraft.client.renderer.Tessellator;
+import net.minecraft.client.renderer.vertex.DefaultVertexFormats;
+import net.minecraft.client.renderer.vertex.VertexBuffer;
+import net.minecraft.client.renderer.vertex.VertexFormat;
 import net.minecraft.world.World;
 import org.spongepowered.asm.mixin.Mixin;
 import org.spongepowered.asm.mixin.Overwrite;
-import org.spongepowered.asm.mixin.Unique;
+import org.spongepowered.asm.mixin.Shadow;
 import org.spongepowered.asm.mixin.injection.At;
 
 /**
@@ -19,8 +24,11 @@
 @Mixin(RenderGlobal.class)
 public class MixinRenderGlobalStars {
 
-    @Unique
-    private int celeritasExtra$prevTotalStars = -1;
+    @Shadow
+    private VertexBuffer starVBO;
+
+    @Shadow
+    private VertexFormat vertexBufferFormat;
 
     /**
      * Control star rendering by wrapping the star brightness calculation.
@@ -49,7 +57,22 @@ private float wrapGetStarBrightness(World world, float partialTicks, Operation<F
      */
     @Overwrite
     private void generateStars() {
+        Tessellator tessellator = Tessellator.getInstance();
+        BufferBuilder buffer = tessellator.getBuffer();
+
+        if (this.starVBO != null) {
+            this.starVBO.deleteGlBuffers();
+        }
+
+        this.starVBO = new VertexBuffer(this.vertexBufferFormat);
+
+        buffer.begin(7, DefaultVertexFormats.POSITION);
+
         int totalStars = CeleritasExtraClientMod.options().detailSettings.totalStars;
-        RenderStars.generateStars(totalStars);
+        RenderStars.generateStars(buffer, totalStars);
+
+        buffer.finishDrawing();
+        buffer.reset();
+        this.starVBO.bufferData(buffer.getByteBuffer());
     }
 }