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-rw-r--r--test/coverage.c20
1 files changed, 13 insertions, 7 deletions
diff --git a/test/coverage.c b/test/coverage.c
index c2dd3986..47280880 100644
--- a/test/coverage.c
+++ b/test/coverage.c
@@ -277,13 +277,19 @@ column_triangles (cairo_t *cr, int width, int height)
* edges on either side that may co-align with their
* neighbours:
*
- * --- . ---
- * 1 / | |\ |
- * / 2x | | \ |
- * --- .... | 1 / x
- * \ | |
- * \| |
- * . ---
+ * s --- . ---
+ * t | |\ |
+ * e | | \ |
+ * p --- .... | 2 * step = 1 / WIDTH
+ * \ | |
+ * \| |
+ * . ---
+ * |---|
+ * 1 / PRECISION
+ *
+ * Each column contains two triangles of width one quantum and
+ * total height of (x / WIDTH), thus the total area covered by all
+ * columns in each pixel is .5 * (x / WIDTH).
*/
cairo_move_to (cr, x + i / (double) PRECISION, y + dy);