ConstructionWand/src/main/java/thetadev/constructionwand/client/RenderBlockPreview.java

package thetadev.constructionwand.client;

import com.mojang.blaze3d.matrix.MatrixStack;
import com.mojang.blaze3d.vertex.IVertexBuilder;
import net.minecraft.client.renderer.IRenderTypeBuffer;
import net.minecraft.client.renderer.WorldRenderer;
import net.minecraft.entity.Entity;
import net.minecraft.entity.player.PlayerEntity;
import net.minecraft.item.ItemStack;
import net.minecraft.util.math.AxisAlignedBB;
import net.minecraft.util.math.BlockPos;
import net.minecraft.util.math.BlockRayTraceResult;
import net.minecraft.util.math.RayTraceResult;
import net.minecraftforge.client.event.DrawHighlightEvent;
import net.minecraftforge.eventbus.api.SubscribeEvent;
import thetadev.constructionwand.basics.WandUtil;
import thetadev.constructionwand.items.wand.ItemWand;
import thetadev.constructionwand.wand.WandJob;

import java.util.Set;

public class RenderBlockPreview
{
    private WandJob wandJob;
    public Set<BlockPos> undoBlocks;

    @SubscribeEvent
    public void renderBlockHighlight(DrawHighlightEvent event) {
        if(event.getTarget().getType() != RayTraceResult.Type.BLOCK) return;

        BlockRayTraceResult rtr = (BlockRayTraceResult) event.getTarget();
        Entity entity = event.getInfo().getRenderViewEntity();
        if(!(entity instanceof PlayerEntity)) return;
        PlayerEntity player = (PlayerEntity) entity;
        Set<BlockPos> blocks;
        float colorR = 0, colorG = 0, colorB = 0;

        ItemStack wand = WandUtil.holdingWand(player);
        if(wand == null) return;

        if(!(player.isCrouching() && ClientEvents.isOptKeyDown())) {
            // Use cached wandJob for previews of the same target pos/dir
            // Exception: always update if blockCount < 2 to prevent 1-block previews when block updates
            // from the last placement are lagging
            if(wandJob == null || !compareRTR(wandJob.rayTraceResult, rtr) || !(wandJob.wand.equals(wand))
                    || wandJob.blockCount() < 2) {
                wandJob = ItemWand.getWandJob(player, player.getEntityWorld(), rtr, wand);
            }
            blocks = wandJob.getBlockPositions();
        }
        else {
            blocks = undoBlocks;
            colorG = 1;
        }

        if(blocks == null || blocks.isEmpty()) return;

        MatrixStack ms = event.getMatrix();
        IRenderTypeBuffer buffer = event.getBuffers();
        IVertexBuilder lineBuilder = buffer.getBuffer(RenderTypes.TRANSLUCENT_LINES);

        double partialTicks = event.getPartialTicks();
        double d0 = player.lastTickPosX + (player.getPosX() - player.lastTickPosX) * partialTicks;
        double d1 = player.lastTickPosY + player.getEyeHeight() + (player.getPosY() - player.lastTickPosY) * partialTicks;
        double d2 = player.lastTickPosZ + (player.getPosZ() - player.lastTickPosZ) * partialTicks;

        ms.push();

        for(BlockPos block : blocks) {
            AxisAlignedBB aabb = new AxisAlignedBB(block).offset(-d0, -d1, -d2);
            WorldRenderer.drawBoundingBox(ms, lineBuilder, aabb, colorR, colorG, colorB, 0.4F);
        }
        ms.pop();

        event.setCanceled(true);
    }

    private static boolean compareRTR(BlockRayTraceResult rtr1, BlockRayTraceResult rtr2) {
        return rtr1.getPos().equals(rtr2.getPos()) && rtr1.getFace().equals(rtr2.getFace());
    }
}