Add back line drawing with bresenham

1 files changed, 27 insertions, 2 deletions

diff --git a/src/renderer_m0.c b/src/renderer_m0.c
index 18d1c5d..2cb7675 100644
--- a/src/renderer_m0.c
+++ b/src/renderer_m0.c
@@ -176,8 +176,26 @@ draw_line(size_t x0, size_t y0, size_t x1, size_t y1, u8 clr) {
         MAYBE_SWAP(y0, y1);
         draw_vline(x0, y0, y1, clr);
     } else {
-        // TODO
-        // // Diagonal line.
+#if 1
+        // Diagonal line.
+        int dx = x0 > x1 ? x0 - x1 : x1 - x0;
+        int dy = y0 > y1 ? y1 - y0 : y0 - y1;
+        int x_step = x0 < x1 ? 1 : -1;
+        int y_step = y0 < y1 ? 1 : -1;
+        int err = dx + dy;
+        while (!(x0 == x1 && y0 == y1)) {
+            draw_pixel(x0, y0, clr);
+            int diff = 2 * err;
+            if (diff >= dy) {
+                err += dy;
+                x0 += x_step;
+            }
+            if (diff <= dx) {
+                err += dx;
+                y0 += y_step;
+            }
+        }
+#else
         // int     dx = x0 > x1 ?       x0 - x1 : x1 - x0;
         // int     dy = y0 > y1 ?       y0 - y1 : y1 - y0;
         // int x_step = x0 > x1 ?            -1 : 1;
@@ -214,6 +232,7 @@ draw_line(size_t x0, size_t y0, size_t x1, size_t y1, u8 clr) {
         //         addr += y_step;
         //     }
         // }
+#endif
     }
 
     // // Find row positions for the given x/y coordinates.
@@ -322,6 +341,12 @@ draw_rect(size_t x0, size_t y0, size_t x1, size_t y1, u8 clr) {
     draw_vline(x0, y0, y1, clr);
     draw_vline(x1, y0, y1, clr);
 #else
+    // NOTE: This is the specialized version trying to update 2 pixels at
+    // a time. As of writing this it is slightly slower than using
+    // 4 draw_hline/vline functions. The horizontal drawing part seems
+    // marginally faster but the vertical one is slower. Potentially the
+    // vertical part could be optimized or just use 2 draw_vline instead. The
+    // perf improvements seem marginal enough that it doesn't seem worth it.
     BOUNDCHECK_SCREEN(x0, y0);
     BOUNDCHECK_SCREEN(x1, y1);
     MAYBE_SWAP(x0, x1);