Reduce work done in CraftMapCanvas.drawImage by limiting size of image and using System.arraycopy instead of for loops and use bitwise operations to do bounds checks.

paper-server/src/main/java/org/bukkit/craftbukkit/map/CraftMapCanvas.java

@@ -91,12 +91,41 @@ public class CraftMapCanvas implements MapCanvas {
 
     @Override
     public void drawImage(int x, int y, Image image) {
-        byte[] bytes = MapPalette.imageToBytes(image);
+        // Paper start - Reduce work done by limiting size of image and using System.arraycopy
-        for (int x2 = 0; x2 < image.getWidth(null); ++x2) {
+        int width = 128 - x;
-            for (int y2 = 0; y2 < image.getHeight(null); ++y2) {
+        int height = 128 - y;
-                this.setPixel(x + x2, y + y2, bytes[y2 * image.getWidth(null) + x2]);
+        if (image.getHeight(null) < height)
+            height = image.getHeight(null);
+
+        // Create a subimage if the image is larger than the max allowed size
+        java.awt.image.BufferedImage temp;
+        if (image.getWidth(null) >= width && image instanceof java.awt.image.BufferedImage bImage) {
+            // If the image is larger than the max allowed size, get a subimage, otherwise use the image as is
+            if (image.getWidth(null) > width || image.getHeight(null) > height) {
+                temp = bImage.getSubimage(0, 0, width, height);
+            } else {
+                temp = bImage;
             }
+        } else {
+            temp = new java.awt.image.BufferedImage(width, height, java.awt.image.BufferedImage.TYPE_INT_ARGB);
+            java.awt.Graphics2D graphics = temp.createGraphics();
+            graphics.drawImage(image, 0, 0, null);
+            graphics.dispose();
         }
+
+        byte[] bytes = MapPalette.imageToBytes(temp);
+        
+        // Since we now control the size of the image, we can safely use System.arraycopy
+        // If x is 0, we can just copy the entire image as width is 128 and height is <=(128-y)
+        if (x == 0) {
+            System.arraycopy(bytes, 0, this.buffer, y * 128, width * height);
+            return;
+        }
+
+        for (int y2 = 0; y2 < height; ++y2) {
+            System.arraycopy(bytes, 0, this.buffer, (y + y2) * 128 + x, width);
+        }
+        // Paper end
     }
 
     @Override

paper-server/src/main/java/org/bukkit/craftbukkit/map/CraftMapRenderer.java

@@ -23,8 +23,10 @@ public class CraftMapRenderer extends MapRenderer {
     @Override
     public void render(MapView map, MapCanvas canvas, Player player) {
         // Map
-        for (int x = 0; x < 128; ++x) {
+        // Paper start - Swap inner and outer loops here to (theoretically) improve cache locality
         for (int y = 0; y < 128; ++y) {
+            for (int x = 0; x < 128; ++x) {
+        // Paper end
                 canvas.setPixel(x, y, this.worldMap.colors[y * 128 + x]);
             }
         }