Fix hline width with custom clip window (#167)

* Fix hline width when using custom clip window
* Fix filled circle test to match fixed hline drawing
* Fix rectangle test to match fixed hline drawing

Author: tuupola

src/hagl_hline.c

@@ -52,7 +52,7 @@ void hagl_draw_hline_xyw(
 
         /* x0 is left of clip window, ignore start part. */
         if (x0 < surface->clip.x0) {
-            width = width + x0;
+            width = width - (surface->clip.x0 - x0);
             x0 = surface->clip.x0;
         }
 

tests/test_circle.c

@@ -430,14 +430,16 @@ TEST test_fill_circle_custom_clip(void) {
     /* Inside clip: center is filled */
     ASSERT_EQ(0xFFFF, hagl_get_pixel(&bitmap, 15, 15));
 
-    /* Inside clip: top corners are filled */
+    /* Inside clip: top-left corner is filled (distance ~7.07 < 10) */
     ASSERT_EQ(0xFFFF, hagl_get_pixel(&bitmap, 10, 10));
-    ASSERT_EQ(0xFFFF, hagl_get_pixel(&bitmap, 25, 10));
+
+    /* Outside circle: top-right corner (distance ~11.18 > 10) */
+    ASSERT_EQ(0x0000, hagl_get_pixel(&bitmap, 25, 10));
 
     /* Inside clip: bottom cardinal */
     ASSERT_EQ(0xFFFF, hagl_get_pixel(&bitmap, 15, 25));
 
-    /* Inside clip: right edge */
+    /* Inside clip: right cardinal */
     ASSERT_EQ(0xFFFF, hagl_get_pixel(&bitmap, 25, 15));
 
     /* Outside clip: clipped cardinals */
@@ -448,8 +450,8 @@ TEST test_fill_circle_custom_clip(void) {
     ASSERT_EQ(0x0000, hagl_get_pixel(&bitmap, 9, 15));
     ASSERT_EQ(0x0000, hagl_get_pixel(&bitmap, 15, 9));
 
-    /* Total: 242 pixels */
-    ASSERT_EQ(242, count_pixels(&bitmap, 0xFFFF));
+    /* Total: 229 pixels */
+    ASSERT_EQ(229, count_pixels(&bitmap, 0xFFFF));
 
     PASS();
 }
@@ -460,7 +462,7 @@ TEST test_fill_circle_custom_clip_regression(void) {
 
     uint32_t crc = crc32(bitmap.buffer, bitmap.size);
 
-    ASSERT_EQ(0xD2A7217B, crc);
+    ASSERT_EQ(0xC468FB33, crc);
     PASS();
 }
 

tests/test_hline.c

@@ -337,6 +337,36 @@ TEST test_draw_hline_xyw_custom_clip_regression(void) {
     PASS();
 }
 
+/*
+ * Line clipped by left edge of custom clip window only:
+ * Line from x=40 to x=59 (width 20) at y=75.
+ * Clip window (50,50)-(200,200). Only x=50..59 visible.
+ *
+ * (40,75)----[50,75)=====(59,75)
+ *             ^clip.x0
+ */
+TEST test_draw_hline_xyw_custom_clip_left(void) {
+    hagl_set_clip(&bitmap, 50, 50, 200, 200);
+    hagl_draw_hline_xyw(&bitmap, 40, 75, 20, 0xFFFF);
+
+    /* On line: left edge of clip window */
+    ASSERT_EQ(0xFFFF, hagl_get_pixel(&bitmap, 50, 75));
+
+    /* On line: right endpoint of original line */
+    ASSERT_EQ(0xFFFF, hagl_get_pixel(&bitmap, 59, 75));
+
+    /* Outside: just left of clip window */
+    ASSERT_EQ(0x0000, hagl_get_pixel(&bitmap, 49, 75));
+
+    /* Outside: just right of original line end */
+    ASSERT_EQ(0x0000, hagl_get_pixel(&bitmap, 60, 75));
+
+    /* Total: 10 pixels */
+    ASSERT_EQ(10, count_pixels(&bitmap, 0xFFFF));
+
+    PASS();
+}
+
 SUITE(hline_suite) {
     SET_SETUP(setup_callback, NULL);
     SET_TEARDOWN(teardown_callback, NULL);
@@ -354,6 +384,7 @@ SUITE(hline_suite) {
     RUN_TEST(test_draw_hline_xyw_outside);
     RUN_TEST(test_draw_hline_xyw_custom_clip);
     RUN_TEST(test_draw_hline_xyw_custom_clip_regression);
+    RUN_TEST(test_draw_hline_xyw_custom_clip_left);
 }
 
 GREATEST_MAIN_DEFS();

tests/test_rectangle.c

@@ -384,9 +384,9 @@ TEST test_draw_rectangle_xyxy_custom_clip(void) {
     ASSERT_EQ(0xFFFF, hagl_get_pixel(&bitmap, 80, 50));
     ASSERT_EQ(0xFFFF, hagl_get_pixel(&bitmap, 80, 65));
 
-    /* On outline: hline/vline extend to clip boundary */
-    ASSERT_EQ(0xFFFF, hagl_get_pixel(&bitmap, 100, 80));
-    ASSERT_EQ(0xFFFF, hagl_get_pixel(&bitmap, 80, 100));
+    /* On outline: hline/vline end at rectangle edge, not clip boundary */
+    ASSERT_EQ(0x0000, hagl_get_pixel(&bitmap, 100, 80));
+    ASSERT_EQ(0x0000, hagl_get_pixel(&bitmap, 80, 100));
 
     /* Inside: interior is empty */
     ASSERT_EQ(0x0000, hagl_get_pixel(&bitmap, 65, 65));
@@ -401,8 +401,8 @@ TEST test_draw_rectangle_xyxy_custom_clip(void) {
     ASSERT_EQ(0x0000, hagl_get_pixel(&bitmap, 49, 80));
     ASSERT_EQ(0x0000, hagl_get_pixel(&bitmap, 80, 49));
 
-    /* Total: right vline 51 + bottom hline 51 - corner 1 = 101 */
-    ASSERT_EQ(101, count_pixels(&bitmap, 0xFFFF));
+    /* Total: right vline 31 + bottom hline 31 - corner 1 = 61 */
+    ASSERT_EQ(61, count_pixels(&bitmap, 0xFFFF));
 
     PASS();
 }
@@ -413,7 +413,7 @@ TEST test_draw_rectangle_xyxy_custom_clip_regression(void) {
 
     uint32_t crc = crc32(bitmap.buffer, bitmap.size);
 
-    ASSERT_EQ(0x876AD58F, crc);
+    ASSERT_EQ(0x17F93E43, crc);
     PASS();
 }