From 40c0489920021195877529ab7bfdf597b9468774 Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Tue, 13 Apr 2021 20:16:02 +0200
Subject: An alternative way of putting pixels on the framebuffer

---
 src/main.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/src/main.c b/src/main.c
index fd5d21a..c49ce51 100644
--- a/src/main.c
+++ b/src/main.c
@@ -20,10 +20,6 @@
 // Display modes.
 //
 
-// Screen settings.
-#define SCREEN_WIDTH 240
-#define SCREEN_HEIGHT 160
-
 // Display modes.
 #define DISP_MODE_0 0x0000
 #define DISP_MODE_1 0x0001
@@ -44,31 +40,38 @@ set_display_mode(u16 value) {
     *((vu32*)(MEM_IO + 0x0000)) = value;
 }
 
-//
-// Colors.
-//
+// Screen settings.
+#define SCREEN_WIDTH 240
+#define SCREEN_HEIGHT 160
 
 // The GBA in mode 3 expects rbg15 colors in the VRAM, where each component
 // (RGB) have a 0--31 range. For example, pure red would be rgb15(31, 0, 0).
 typedef u16 Color;
 
+// We can treat the screen as a HxW matrix. With the following macro we can
+// write a pixel to the screen at the (x, y) position using:
+//
+//     FRAMEBUFFER[y][x] = color;
+//
+typedef Color Scanline[SCREEN_WIDTH];
+#define FRAMEBUFFER ((Scanline*)MEM_VRAM)
+
+//
+// Colors.
+//
+
 static inline Color
 rgb15(u32 red, u32 green, u32 blue ) {
     return (blue << 10) | (green << 5) | red;
 }
 
-static inline void
-put_pixel(int x, int y, Color clr) {
-    ((vu16*)MEM_VRAM)[x + y * SCREEN_WIDTH] = clr;
-}
-
 // Using bd-font, an 8x8 bitmap font.
 static inline 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) {
             if ((font[chr][i] >> (7 - j)) & 0x1) {
-                put_pixel(x + j, y + i, clr);
+                FRAMEBUFFER[y + i][x + j] = clr;
             }
         }
     }
@@ -90,7 +93,6 @@ put_line(int x, int y, Color clr, char *msg) {
 int main(void) {
     set_display_mode(DISP_MODE_3 | DISP_BG2);
 
-
     while(true) {
         put_line(16,  20 + 16, rgb15(28, 0, 0), "Hello world from the GBA!");
         put_line(16,  20 + 32, rgb15(0, 28, 28), "Using my little 8x8 bd-font");
-- 
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