Graphics renderer fix : math problem: java

The problem is v. v. small and the fix will only be a few lines of code. The problem is more mathematical than tech related. The code is drawing a grid of images to the screen : overdraw beyond the screen clip is prevented using a full draw call public void drawImage(Image img, double sx, double sy, double sw, double sh, double dx, double dy, double dw, double dh) the existing solution is complete and working. But it doesn't scale. It needs to scale the graphics by a Java 'double'. There is a ready test program that's only a 100 lines. The actual problem code is maybe 20 lines long and revolves around rectangle intersection. Some knowledge of JavaFX or Swing would help, but it's the algorithm that needs a fix. This should take an expert one hour max.