pnmimage: Added offset to add_sub_image and mult_sub_image

Closes #903

panda/src/pnmimage/pnmImage.cxx

@@ -1176,7 +1176,7 @@ add_sub_image(const PNMImage &copy, int xto, int yto,
   if (has_alpha() && copy.has_alpha()) {
     for (y = ymin; y < ymax; y++) {
       for (x = xmin; x < xmax; x++) {
-        set_alpha(x, y, get_alpha(x, y) + copy.get_alpha(x, y) * pixel_scale);
+        set_alpha(x, y, get_alpha(x, y) + copy.get_alpha(x - xmin + xfrom, y - ymin + yfrom) * pixel_scale);
       }
     }
   }
@@ -1184,7 +1184,7 @@ add_sub_image(const PNMImage &copy, int xto, int yto,
   for (y = ymin; y < ymax; y++) {
     for (x = xmin; x < xmax; x++) {
       LRGBColorf rgb1 = get_xel(x, y);
-      LRGBColorf rgb2 = copy.get_xel(x, y);
+      LRGBColorf rgb2 = copy.get_xel(x - xmin + xfrom, y - ymin + yfrom);
       set_xel(x, y,
               rgb1[0] + rgb2[0] * pixel_scale,
               rgb1[1] + rgb2[1] * pixel_scale,
@@ -1210,7 +1210,7 @@ mult_sub_image(const PNMImage &copy, int xto, int yto,
   if (has_alpha() && copy.has_alpha()) {
     for (y = ymin; y < ymax; y++) {
       for (x = xmin; x < xmax; x++) {
-        set_alpha(x, y, get_alpha(x, y) * copy.get_alpha(x, y) * pixel_scale);
+        set_alpha(x, y, get_alpha(x, y) * copy.get_alpha(x - xmin + xfrom, y - ymin + yfrom) * pixel_scale);
       }
     }
   }
@@ -1218,7 +1218,7 @@ mult_sub_image(const PNMImage &copy, int xto, int yto,
   for (y = ymin; y < ymax; y++) {
     for (x = xmin; x < xmax; x++) {
       LRGBColorf rgb1 = get_xel(x, y);
-      LRGBColorf rgb2 = copy.get_xel(x, y);
+      LRGBColorf rgb2 = copy.get_xel(x - xmin + xfrom, y - ymin + yfrom);
       set_xel(x, y,
               rgb1[0] * rgb2[0] * pixel_scale,
               rgb1[1] * rgb2[1] * pixel_scale,

tests/pnmimage/test_pnmimage.py

@@ -70,3 +70,40 @@ def test_pnmimage_quantize():
             assert col.b in (0, 1)
 
     assert max_dist < 0.1 ** 2
+
+def test_pnmimage_add_sub_image():
+    dst = PNMImage(2, 2)
+    dst.fill(0.5, 0, 0)   #adding color to dst
+    #dst_color will store rgb values at each pixel of dst
+    dst_color = ((dst.get_xel(0, 0), dst.get_xel(0, 1)), (dst.get_xel(1, 0), dst.get_xel(1, 1)))
+
+    src = PNMImage(1, 1)
+    src.fill(0, 0.7, 0)   #adding color to src
+    #src_color will store rgb values at each pixel of src
+    src_color = src.get_xel(0, 0)
+
+    dst.add_sub_image(src, 1, 1, 0, 0, 1, 1)
+    final_color = ((dst.get_xel(0, 0), dst.get_xel(0, 1)), (dst.get_xel(1, 0), dst.get_xel(1, 1)))
+    assert final_color[0][0] == dst_color[0][0]
+    assert final_color[0][1] == dst_color[0][1]
+    assert final_color[1][0] == dst_color[1][0]
+    assert final_color[1][1] == dst_color[1][1] + src_color
+
+
+def test_pnmimage_mult_sub_image():
+    dst = PNMImage(2, 2)
+    dst.fill(0.5, 0, 0)   #adding color to dst
+    #dst_color will store rgb values at each pixel of dst
+    dst_color = ((dst.get_xel(0, 0), dst.get_xel(0, 1)), (dst.get_xel(1, 0), dst.get_xel(1, 1)))
+
+    src = PNMImage(1, 1)
+    src.fill(0, 0.7, 0)   #adding color to src
+    #src_color will store rgb values at each pixel of src
+    src_color = src.get_xel(0, 0)
+
+    dst.mult_sub_image(src, 1, 1, 0, 0, 1, 1)
+    final_color = ((dst.get_xel(0, 0), dst.get_xel(0, 1)), (dst.get_xel(1, 0), dst.get_xel(1, 1)))
+    assert final_color[0][0] == dst_color[0][0]
+    assert final_color[0][1] == dst_color[0][1]
+    assert final_color[1][0] == dst_color[1][0]
+    assert final_color[1][1][0] == dst_color[1][1][0] * src_color[0] and final_color[1][1][1] == dst_color[1][1][1] * src_color[1] and final_color[1][1][2] == dst_color[1][1][2] * src_color[2]