From ff99878755fd12e93664471aa4f01fe1a4e677ef Mon Sep 17 00:00:00 2001
From: Yousef Khadadeh <erroratline0@gmail.com>
Date: Sat, 6 Jun 2026 14:43:24 +0300
Subject: [PATCH] Fixed eraser tool adding to mesh in rare cases

---
 src/CanvasComponents/MeshCanvasComponent.cpp | 15 ++++++++++-----
 src/DrawingProgram/Tools/EraserTool.cpp      | 14 ++++++++++----
 src/DrawingProgram/Tools/EraserTool.hpp      |  1 +
 3 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/src/CanvasComponents/MeshCanvasComponent.cpp b/src/CanvasComponents/MeshCanvasComponent.cpp
index e3e9a49..e122422 100644
--- a/src/CanvasComponents/MeshCanvasComponent.cpp
+++ b/src/CanvasComponents/MeshCanvasComponent.cpp
@@ -374,13 +374,18 @@ CanvasComponentEraseDetailResult MeshCanvasComponent::erase_detail(const SkPath&
     bool intersectsAABB = d.meshPath.getBounds().intersects(eraseAgainst.getBounds());
     if(!intersectsAABB)
         return CanvasComponentEraseDetailResult::NO_CHANGE;
-    std::optional<SkPath> newPath = Op(d.meshPath, eraseAgainst, SkPathOp::kDifference_SkPathOp);
+    std::optional<SkPath> newPath = Op(Simplify(d.meshPath).value(), Simplify(eraseAgainst).value(), SkPathOp::kDifference_SkPathOp);
     if(newPath.has_value()) {
-        auto oldPath = d.meshPath;
-        d.meshPath = newPath.value();
-        if(d.meshPath.isEmpty())
+        if(newPath.value().isEmpty()) {
+            d.meshPath = newPath.value();
             return CanvasComponentEraseDetailResult::REMOVED;
-        return CanvasComponentEraseDetailResult::CHANGED;
+        }
+        else if(!d.meshPath.getBounds().contains(newPath.value().getBounds())) // If bounds of erased path is larger than bounds of original path (can happen when difference op bugs out with big eraser paths), dont change the path
+            return CanvasComponentEraseDetailResult::NO_CHANGE;
+        else {
+            d.meshPath = newPath.value();
+            return CanvasComponentEraseDetailResult::CHANGED;
+        }
     }
     return CanvasComponentEraseDetailResult::NO_CHANGE;
 }
diff --git a/src/DrawingProgram/Tools/EraserTool.cpp b/src/DrawingProgram/Tools/EraserTool.cpp
index bf5864d..7488b67 100644
--- a/src/DrawingProgram/Tools/EraserTool.cpp
+++ b/src/DrawingProgram/Tools/EraserTool.cpp
@@ -89,17 +89,18 @@ void EraserTool::input_mouse_button_on_canvas_callback(const InputManager::Mouse
             BrushComponentCode::mouse_button(drawP, genData, drawP.world.drawData.cam.c, button, relativeWidthResult.first.value());
             // NOTE: Must set erase path when isErasing is set to true to make sure that the Circle path from not erasing part doesn't reach the erase_on_path code
             erasePath = BrushComponentCode::brush_stroke_to_skpath(genData.brushPoints, drawP.world.main.toolConfig.brush.hasRoundCaps);
-            isErasing = true;
+            eraserChanged = isErasing = true;
         }
         else if(!button.down && isErasing) {
             // If not real time eraser, we can benefit from simplifying the path
             std::optional<SkPath> simplified = Simplify(erasePath);
             if(simplified.has_value())
                 erasePath = simplified.value();
-            erase_on_path();
+            if(eraserChanged)
+                erase_on_path();
             reset_erasing_stroke();
             commit_erase();
-            isErasing = false;
+            eraserChanged = isErasing = false;
         }
     }
 }
@@ -108,6 +109,7 @@ void EraserTool::input_mouse_motion_callback(const InputManager::MouseMotionCall
     if(isErasing) {
         auto& toolConfig = drawP.world.main.toolConfig;
         BrushComponentCode::mouse_motion(drawP, genData, motion.pos, toolConfig.get_relative_width_stroke_size(drawP, genData.coords.inverseScale).first.value());
+        eraserChanged = true;
     }
 }
 
@@ -118,6 +120,7 @@ void EraserTool::input_pen_axis_callback(const InputManager::PenAxisCallbackArgs
             auto& toolConfig = drawP.world.main.toolConfig;
             float width = toolConfig.get_relative_width_stroke_size(drawP, genData.coords.inverseScale).first.value();
             BrushComponentCode::pen_pressure(drawP, genData, width);
+            eraserChanged = true;
         }
     }
 }
@@ -281,7 +284,10 @@ void EraserTool::commit_data() {
     if(isErasing) {
         erasePath = BrushComponentCode::brush_stroke_to_skpath(genData.brushPoints, drawP.world.main.toolConfig.brush.hasRoundCaps);
         if(drawP.world.main.conf.realTimeEraser) {
-            erase_on_path();
+            if(eraserChanged) {
+                erase_on_path();
+                eraserChanged = false;
+            }
             reset_erasing_stroke();
         }
     }
diff --git a/src/DrawingProgram/Tools/EraserTool.hpp b/src/DrawingProgram/Tools/EraserTool.hpp
index 1c14416..bec4a4d 100644
--- a/src/DrawingProgram/Tools/EraserTool.hpp
+++ b/src/DrawingProgram/Tools/EraserTool.hpp
@@ -56,4 +56,5 @@ class EraserTool : public DrawingProgramToolBase {
         void commit_erase();
         void commit_data();
         bool isErasing = false;
+        bool eraserChanged = false;
 };