NeoForge/patches/net/minecraft/client/renderer/ItemInHandRenderer.java.patch

--- a/net/minecraft/client/renderer/ItemInHandRenderer.java
+++ b/net/minecraft/client/renderer/ItemInHandRenderer.java
@@ -157,11 +_,11 @@
         Identifier skinTexture = this.minecraft.player.getSkin().body().texturePath();
         if (arm == HumanoidArm.RIGHT) {
             avatarRenderer.renderRightHand(
-                poseStack, submitNodeCollector, lightCoords, skinTexture, this.minecraft.player.isModelPartShown(PlayerModelPart.RIGHT_SLEEVE)
+                poseStack, submitNodeCollector, lightCoords, skinTexture, this.minecraft.player.isModelPartShown(PlayerModelPart.RIGHT_SLEEVE), this.minecraft.player
             );
         } else {
             avatarRenderer.renderLeftHand(
-                poseStack, submitNodeCollector, lightCoords, skinTexture, this.minecraft.player.isModelPartShown(PlayerModelPart.LEFT_SLEEVE)
+                poseStack, submitNodeCollector, lightCoords, skinTexture, this.minecraft.player.isModelPartShown(PlayerModelPart.LEFT_SLEEVE), this.minecraft.player
             );
         }
 
@@ -231,7 +_,7 @@
         poseStack.translate(-0.5F, -0.5F, 0.0F);
         poseStack.scale(0.0078125F, 0.0078125F, 0.0078125F);
         MapId id = itemStack.get(DataComponents.MAP_ID);
-        MapItemSavedData data = MapItem.getSavedData(id, this.minecraft.level);
+        MapItemSavedData data = MapItem.getSavedData(itemStack, this.minecraft.level);
         RenderType renderType = data == null ? MAP_BACKGROUND : MAP_BACKGROUND_CHECKERBOARD;
         submitNodeCollector.submitCustomGeometry(poseStack, renderType, (pose, buffer) -> {
             buffer.addVertex(pose, -7.0F, 135.0F, 0.0F).setColor(-1).setUv(0.0F, 1.0F).setLight(lightCoords);
@@ -270,9 +_,9 @@
         AvatarRenderer<AbstractClientPlayer> avatarRenderer = this.entityRenderDispatcher.getPlayerRenderer(player);
         Identifier skinTexture = player.getSkin().body().texturePath();
         if (isRightArm) {
-            avatarRenderer.renderRightHand(poseStack, submitNodeCollector, lightCoords, skinTexture, player.isModelPartShown(PlayerModelPart.RIGHT_SLEEVE));
+            avatarRenderer.renderRightHand(poseStack, submitNodeCollector, lightCoords, skinTexture, player.isModelPartShown(PlayerModelPart.RIGHT_SLEEVE), player);
         } else {
-            avatarRenderer.renderLeftHand(poseStack, submitNodeCollector, lightCoords, skinTexture, player.isModelPartShown(PlayerModelPart.LEFT_SLEEVE));
+            avatarRenderer.renderLeftHand(poseStack, submitNodeCollector, lightCoords, skinTexture, player.isModelPartShown(PlayerModelPart.LEFT_SLEEVE), player);
         }
     }
 
@@ -345,6 +_,7 @@
             float mainHandAttack = attackHand == InteractionHand.MAIN_HAND ? attackValue : 0.0F;
             float mainhandInverseArmHeight = this.itemModelResolver.swapAnimationScale(this.mainHandItem)
                 * (1.0F - Mth.lerp(frameInterp, this.oMainHandHeight, this.mainHandHeight));
+            if(!net.neoforged.neoforge.client.ClientHooks.renderSpecificFirstPersonHand(InteractionHand.MAIN_HAND, poseStack, submitNodeCollector, lightCoords, frameInterp, xRot, mainHandAttack, mainhandInverseArmHeight, this.mainHandItem))
             this.submitArmWithItem(
                 player,
                 frameInterp,
@@ -363,6 +_,7 @@
             float offHandAttack = attackHand == InteractionHand.OFF_HAND ? attackValue : 0.0F;
             float offhandInverseArmHeight = this.itemModelResolver.swapAnimationScale(this.offHandItem)
                 * (1.0F - Mth.lerp(frameInterp, this.oOffHandHeight, this.offHandHeight));
+            if(!net.neoforged.neoforge.client.ClientHooks.renderSpecificFirstPersonHand(InteractionHand.OFF_HAND, poseStack, submitNodeCollector, lightCoords, frameInterp, xRot, offHandAttack, offhandInverseArmHeight, this.offHandItem))
             this.submitArmWithItem(
                 player,
                 frameInterp,
@@ -431,13 +_,13 @@
                 if (isMainHand && !player.isInvisible()) {
                     this.renderPlayerArm(poseStack, submitNodeCollector, lightCoords, inverseArmHeight, attack, arm);
                 }
-            } else if (itemStack.has(DataComponents.MAP_ID)) {
+            } else if (itemStack.getItem() instanceof MapItem) {
                 if (isMainHand && this.offHandItem.isEmpty()) {
                     this.renderTwoHandedMap(poseStack, submitNodeCollector, lightCoords, xRot, inverseArmHeight, attack);
                 } else {
                     this.renderOneHandedMap(poseStack, submitNodeCollector, lightCoords, inverseArmHeight, arm, attack, itemStack);
                 }
-            } else if (itemStack.is(Items.CROSSBOW)) {
+            } else if (itemStack.getItem() instanceof CrossbowItem) {
                 this.applyItemArmTransform(poseStack, arm, inverseArmHeight);
                 boolean charged = CrossbowItem.isCharged(itemStack);
                 boolean isRightArm = arm == HumanoidArm.RIGHT;
@@ -482,6 +_,8 @@
             } else {
                 boolean isRightArm = arm == HumanoidArm.RIGHT;
                 int invert = isRightArm ? 1 : -1;
+                // Neo: Allow items to define custom arm animation
+                if (!net.neoforged.neoforge.client.extensions.common.IClientItemExtensions.of(itemStack).applyForgeHandTransform(poseStack, minecraft.player, arm, itemStack, frameInterp, inverseArmHeight, attack))
                 if (player.isUsingItem() && player.getUseItemRemainingTicks() > 0 && player.getUsedItemHand() == hand) {
                     ItemUseAnimation useAnimation = itemStack.getUseAnimation();
                     if (!useAnimation.hasCustomArmTransform()) {
@@ -629,9 +_,18 @@
             this.mainHandHeight = Mth.clamp(this.mainHandHeight - 0.4F, 0.0F, 1.0F);
             this.offHandHeight = Mth.clamp(this.offHandHeight - 0.4F, 0.0F, 1.0F);
         } else {
+            // Neo: allow suppressing re-equip animation when only the stack's data changes
+            boolean swapAnimMain = net.neoforged.neoforge.client.ClientHooks.shouldCauseReequipAnimation(this.mainHandItem, nextMainHand, player.getInventory().getSelectedSlot());
+            boolean swapAnimOff = net.neoforged.neoforge.client.ClientHooks.shouldCauseReequipAnimation(this.offHandItem, nextOffHand, -1);
+
+            if (!swapAnimMain && this.mainHandItem != nextMainHand)
+                this.mainHandItem = nextMainHand;
+            if (!swapAnimOff && this.offHandItem != nextOffHand)
+                this.offHandItem = nextOffHand;
+
             float attackAnim = player.getItemSwapScale(1.0F);
-            float mainHandTargetHeight = this.mainHandItem != nextMainHand ? 0.0F : attackAnim * attackAnim * attackAnim;
-            float offHandTargetHeight = this.offHandItem != nextOffHand ? 0.0F : 1.0F;
+            float mainHandTargetHeight = swapAnimMain ? 0.0F : attackAnim * attackAnim * attackAnim;
+            float offHandTargetHeight = swapAnimOff ? 0.0F : 1.0F;
             this.mainHandHeight = this.mainHandHeight + Mth.clamp(mainHandTargetHeight - this.mainHandHeight, -0.4F, 0.4F);
             this.offHandHeight = this.offHandHeight + Mth.clamp(offHandTargetHeight - this.offHandHeight, -0.4F, 0.4F);
         }