Adapt TONC routine for line drawing

2 files changed, 27 insertions, 43 deletions

diff --git a/src/main.c b/src/main.c
index d81a26a..1982992 100644
--- a/src/main.c
+++ b/src/main.c
@@ -135,6 +135,14 @@ int main(void) {
         // draw_line(100, 0, 0, 50, 1);
         // // draw_line(100, 0, 0, 100, 2);
         // // draw_line(50,  0, 0, 100, 3);
+        // draw_line(0, 0, 50, 159, 1);
+        // draw_line(0, 0, 50, 159, 1);
+        // draw_line(1, 1, 50, 159, 2);
+        // draw_line(2, 2, 50, 159, 1);
+        // draw_line(3, 3, 50, 159, 2);
+        // draw_line(4, 4, 50, 159, 1);
+        // draw_line(5, 5, 50, 159, 2);
+        // draw_line(50, 159, 0, 0, 1);
         // txt_render();
         // txt_clear();
             // txt_printf("dx: %d\n", dx);
diff --git a/src/renderer_m4.c b/src/renderer_m4.c
index c950763..28fdd1f 100644
--- a/src/renderer_m4.c
+++ b/src/renderer_m4.c
@@ -146,67 +146,43 @@ 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 {
-#if 1
         // Diagonal line.
-        if (x0 > x1) {
-            SWAP(x0, x1);
-            SWAP(y0, y1);
-        }
-        int dx = x1 - x0;
-        int dy = y0 > y1 ? y0 - y1 : y1 - y0;
-        int x_step = 1;
-        int y_step = y0 > y1 ? -1 : 1;
-        y_step *= SCREEN_WIDTH / 2;
-
-        // Mini-LUT for M4 byte decoding.
-        u16 mask[]   = { ~0xFF,         0xFF };
-        u16 color[]  = {   clr,   (clr << 8) };
-        u8 advance[] = {     0,       x_step };
-        u16 *dst = &backbuf[(x0 + y0 * SCREEN_WIDTH) / 2];
+        int     dx = x0 > x1 ?       x0 - x1 : x1 - x0;
+        int     dy = y0 > y1 ?       y0 - y1 : y1 - y0;
+        int x_step = x0 > x1 ?            -1 : 1;
+        int y_step = y0 > y1 ? -SCREEN_WIDTH : SCREEN_WIDTH;
+
+        u32 addr = (u32)((u32)backbuf + (y0 * SCREEN_WIDTH + x0));
+        u16 *dst = NULL;
+        u32 mask = x0 & 1 ? ~0xFF : 0xFF;
+        u32 color = (clr & 0xFF) | ((clr & 0xFF) << 8);
         if (dx >= dy) {
             int diff = 2 * dy - dx;
             for (int i = dx; i >= 0; i--) {
-                *dst = (*dst & mask[x0 & 1]) | color[x0 & 1];
+                dst = (u16 *)(addr - (mask >> 31));
+                *dst = (*dst & ~mask) | (color & mask);
                 if (diff >= 0) {
                     diff -= 2 * dx;
-                    dst = dst + y_step;
+                    addr += y_step;
                 }
                 diff += 2 * dy;
-                dst = dst + advance[x0 & 1];
-                x0 += x_step;
+                addr += x_step;
+                mask = ~mask;
             }
         } else {
             int diff = 2 * dx - dy;
             for (int i = dy; i >= 0; i--) {
-                *dst = (*dst & mask[x0 & 1]) | color[x0 & 1];
+                dst = (u16 *)(addr - (mask >> 31));
+                *dst = (*dst & ~mask) | (color & mask);
                 if (diff >= 0) {
                     diff -= 2 * dy;
-                    dst = dst + advance[x0 & 1];
-                    x0 += x_step;
+                    addr += x_step;
+                    mask = ~mask;
                 }
                 diff += 2 * dx;
-                dst = dst + y_step;
-            }
-        }
-#else
-        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;
+                addr += y_step;
             }
         }
-#endif
     }
     screen_updated = true;
 }