1 files changed, 55 insertions, 51 deletions

diff --git a/src/main.c b/src/main.c
index 0261e8a..b86a830 100644
--- a/src/main.c
+++ b/src/main.c
@@ -78,7 +78,7 @@ rgb15(u32 red, u32 green, u32 blue ) {
 #define COLOR_WHITE rgb15(28, 28, 28)
 
 // Using bd-font, an 8x8 bitmap font.
-static inline void
+static void
 put_char(int x, int y, Color clr, u8 chr) {
     for (size_t i = 0; i < 8; ++i) {
         for (size_t j = 0; j < 8; ++j) {
@@ -89,7 +89,7 @@ put_char(int x, int y, Color clr, u8 chr) {
     }
 }
 
-static inline void
+static void
 put_text(int x, int y, Color clr, char *msg) {
     int count = 0;
     while (*msg) {
@@ -100,69 +100,73 @@ put_text(int x, int y, Color clr, char *msg) {
 
 // Draws a line with the given color between (x0,y0) and (x1,y1) using the
 // Bresenham's line drawing algorithm using exclusively integer arithmetic.
-static inline void
+static void
 draw_line(int x0, int y0, int x1, int y1, Color clr) {
-    // Keep track of the coordinate for writing to the memory buffer.
-    int x = x0;
-    int y = y0;
+    // The line length in color units.
+    int pitch = SCREEN_WIDTH;
+
+    // Pointer to the initial position of the screen buffer where we will start
+    // writing our data. We need to multiply by 2 because in mode 3 we have
+    // 2 bytes per pixel.
+    vu16 *destination = (u16*)(SCREEN_BUFFER + y0 * pitch * 2 + x0 * 2);
 
     // Adjust the step direction and calculate deltas.
-    int x_step = 1;
-    int y_step = 1;
-    int dx = x1 - x0;
-    int dy = y1 - y0;
+    int x_step;
+    int dx;
     if (x0 > x1) {
         x_step = -1;
         dx = x0 - x1;
+    } else {
+        x_step = 1;
+        dx = x1 - x0;
     }
+    int y_step;
+    int dy;
     if (y0 > y1) {
-        y_step = -1;
+        y_step = -pitch;
         dy = y0 - y1;
+    } else {
+        y_step = +pitch;
+        dy = y1 - y0;
     }
 
     // Precalculate 2 * deltas for x and y.
     int ddx = dx + dx;
     int ddy = dy + dy;
 
-    // These variables are dependant on the slope. We can avoid considering
-    // separate cases for positive and negative slopes by using pointers to
-    // update the step in x or y.
-    int diff;
-    int diff_inc_a;
-    int diff_inc_b;
-    int n_steps;
-    int *a;
-    int *b;
-    int a_step;
-    int b_step;
-    if (dx >= dy) {
-        diff = ddy - dx;
-        diff_inc_a = ddy;
-        diff_inc_b = ddx;
-        n_steps = dx;
-        a = &x;
-        b = &y;
-        a_step = x_step;
-        b_step = y_step;
+    if(dy == 0) {
+        // Horizontal line.
+        for(int i = 0; i <= dx; i++) {
+            destination[i * x_step] = clr;
+        }
+    } else if(dx == 0) {
+        // Vertical line.
+        for(int i = 0; i <= dy; i++) {
+            destination[i * y_step] = clr;
+        }
+    } else if (dx >= dy){
+        // Positive slope.
+        int diff = ddy - dx;
+        for (int i = 0; i <= dx; ++i) {
+            *destination = clr;
+            if (diff >= 0) {
+                destination += y_step;
+                diff -= ddx;
+            }
+            destination += x_step;
+            diff += ddy;
+        }
     } else {
-        diff = ddx - dy;
-        diff_inc_a = ddx;
-        diff_inc_b = ddy;
-        n_steps = dy;
-        a = &y;
-        b = &x;
-        a_step = y_step;
-        b_step = x_step;
-    }
-
-    // Draw the line with Bresenham's algorithm.
-    for (int i = 0; i <= n_steps; ++i) {
-        FRAMEBUFFER[y][x] = clr;
-        *a += a_step;
-        diff += diff_inc_a;
-        if (diff > 0) {
-            *b += b_step;
-            diff -= diff_inc_b;
+        // Negative slope.
+        int diff = ddx - dy;
+        for (int i = 0; i <= dy; ++i) {
+            *destination = clr;
+            if (diff >= 0) {
+                destination += x_step;
+                diff -= ddy;
+            }
+            destination += y_step;
+            diff += ddx;
         }
     }
 }
@@ -233,7 +237,7 @@ wait_vsync() {
 // GBA needs to meet memory alignment requirements, we can't write a u8 into
 // memory, instead we need to read a u16 word, mask and or the corresponding
 // bits and wave the updated u16.
-static inline void
+static void
 put_pixel_m4(int x, int y, u8 col_index, vu16 *buffer) {
     int buffer_index = (y * SCREEN_WIDTH + x) / 2;
     vu16 *destination = &buffer[buffer_index];
@@ -247,7 +251,7 @@ put_pixel_m4(int x, int y, u8 col_index, vu16 *buffer) {
     }
 }
 
-static inline void
+static void
 draw_fill_rect_m4(int x0, int y0, int x1, int y1, u8 col_index, vu16 *buffer) {
     int ix, iy;
     for(iy = y0; iy < y1; iy++) {