Implement BitmapData.scroll()

core/src/avm1/globals/bitmap_data.rs

@@ -656,13 +656,26 @@ pub fn pixel_dissolve<'gc>(
 }
 
 pub fn scroll<'gc>(
-    _activation: &mut Activation<'_, 'gc, '_>,
+    activation: &mut Activation<'_, 'gc, '_>,
     this: Object<'gc>,
-    _args: &[Value<'gc>],
+    args: &[Value<'gc>],
 ) -> Result<Value<'gc>, Error<'gc>> {
     if let Some(bitmap_data) = this.as_bitmap_data_object() {
         if !bitmap_data.disposed() {
-            log::warn!("BitmapData.scroll - not yet implemented");
+            let x = args
+                .get(0)
+                .unwrap_or(&Value::Undefined)
+                .coerce_to_i32(activation)?;
+            let y = args
+                .get(1)
+                .unwrap_or(&Value::Undefined)
+                .coerce_to_i32(activation)?;
+
+            bitmap_data
+                .bitmap_data()
+                .write(activation.context.gc_context)
+                .scroll(x, y);
+
             return Ok(Value::Undefined);
         }
     }

core/src/avm1/object/bitmap_data.rs

@@ -481,6 +481,48 @@ impl BitmapData {
 
         (x, y, w, h)
     }
+
+    pub fn scroll(&mut self, x: i32, y: i32) {
+        let width = self.width() as i32;
+        let height = self.height() as i32;
+
+        if (x == 0 && y == 0) || x.abs() >= width || y.abs() >= height {
+            return; // no-op
+        }
+
+        // since this is an "in-place copy", we have to iterate from bottom to top
+        // when scrolling downwards - so if y is positive
+        let reverse_y = y > 0;
+        // and if only scrolling horizontally, we have to iterate from right to left
+        // when scrolling right - so if x is positive
+        let reverse_x = y == 0 && x > 0;
+
+        // iteration ranges to use as source for the copy, from is inclusive, to is exclusive
+        let y_from = if reverse_y { height - y - 1 } else { -y };
+        let y_to = if reverse_y { -1 } else { height };
+        let dy = if reverse_y { -1 } else { 1 };
+
+        let x_from = if reverse_x {
+            // we know x > 0
+            width - x - 1
+        } else {
+            // x can be any sign
+            (-x).max(0)
+        };
+        let x_to = if reverse_x { -1 } else { width.min(width - x) };
+        let dx = if reverse_x { -1 } else { 1 };
+
+        let mut src_y = y_from;
+        while src_y != y_to {
+            let mut src_x = x_from;
+            while src_x != x_to {
+                let color = self.get_pixel_raw(src_x as u32, src_y as u32).unwrap();
+                self.set_pixel32_raw((src_x + x) as u32, (src_y + y) as u32, color);
+                src_x += dx;
+            }
+            src_y += dy;
+        }
+    }
 }
 
 /// A BitmapData