Add Framebuffer.copy_rows_up()

src/hulk/framebuffer.d

@@ -168,6 +168,20 @@ struct Framebuffer
         blend_alpha_bitmap(x, y, alpha_bitmap.ptr, width, height, color);
     }
 
+    /**
+     * Copy framebuffer rows up in the framebuffer.
+     *
+     * @param y Y coordinate of bottom side of region to copy up.
+     * @param height Height of region to copy up.
+     * @param offset Number of rows to copy region up by.
+     */
+    void copy_rows_up(size_t y, size_t height, size_t offset)
+    {
+        memcpy32(&m_buffer[buffer_index(0u, y + height + offset - 1u)],
+                 &m_buffer[buffer_index(0u, y + height - 1u)],
+                 (m_stride * height));
+    }
+
     /**
      * Scale a color value by an alpha amount.
      *