Use hardware copy for render target blits where possible

Minecraft performs a blit using a fragment shader, which
is unnecessary when blending is not used. Using the fixed
function hardware to perform the blit is much faster and
doesn't utilize the rasterization engine.

This is a cherry-pick of cd18e7f, 1ac46d0, and e1bae36.

src/main/java/me/jellysquid/mods/sodium/client/data/config/MixinConfig.java

@@ -51,6 +51,8 @@ private MixinConfig() {
 
         this.addMixinRule("features.render", true);
 
+        this.addMixinRule("features.render.compositing", true);
+
         this.addMixinRule("features.render.entity", true);
         this.addMixinRule("features.render.entity.cull", true);
         this.addMixinRule("features.render.entity.shadow", true);

src/main/java/me/jellysquid/mods/sodium/mixin/features/render/compositing/FramebufferMixin.java

@@ -0,0 +1,48 @@
+package me.jellysquid.mods.sodium.mixin.features.render.compositing;
+
+
+import net.caffeinemc.mods.sodium.client.compatibility.workarounds.Workarounds;
+import net.minecraft.client.gl.Framebuffer;
+import org.lwjgl.opengl.GL32C;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+@Mixin(Framebuffer.class)
+public class FramebufferMixin {
+    @Shadow
+    public int fbo;
+
+    @Shadow
+    public int textureWidth;
+
+    @Shadow
+    public int textureHeight;
+
+    /**
+     * @author JellySquid
+     * @reason Use fixed function hardware for framebuffer blits
+     */
+    @Inject(method = "drawInternal", at = @At("HEAD"), cancellable = true)
+    public void blitToScreen(int width, int height, boolean disableBlend, CallbackInfo ci) {
+        if (Workarounds.isWorkaroundEnabled(Workarounds.Reference.INTEL_FRAMEBUFFER_BLIT_CRASH_WHEN_UNFOCUSED)) {
+            return;
+        }
+
+        if (disableBlend) {
+            ci.cancel();
+
+            // When blending is not used, we can directly copy the contents of one
+            // framebuffer to another using the blitting engine. This can save a lot of time
+            // when compared to going through the rasterization pipeline.
+            GL32C.glBindFramebuffer(GL32C.GL_READ_FRAMEBUFFER, this.fbo);
+            GL32C.glBlitFramebuffer(
+                    0, 0, width, height,
+                    0, 0, width, height,
+                    GL32C.GL_COLOR_BUFFER_BIT, GL32C.GL_LINEAR);
+            GL32C.glBindFramebuffer(GL32C.GL_READ_FRAMEBUFFER, 0);
+        }
+    }
+}

src/main/resources/sodium.mixins.json

@@ -44,6 +44,7 @@
     "features.options.render_layers.LeavesBlockMixin",
     "features.options.render_layers.RenderLayersMixin",
     "features.options.weather.WorldRendererMixin",
+    "features.render.compositing.FramebufferMixin",
     "features.render.entity.CuboidMixin",
     "features.render.entity.ModelPartMixin",
     "features.render.entity.cull.EntityRendererMixin",