From 05f557f302ce566247c37619b130ebebae2a39c8 Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Thu, 15 Apr 2021 18:18:05 +0200
Subject: Add tests for page flipping on mode 4

---
 src/main.c | 37 ++++++++++++++++++++++++++-----------
 1 file changed, 26 insertions(+), 11 deletions(-)

diff --git a/src/main.c b/src/main.c
index 7c33166..2a6abb3 100644
--- a/src/main.c
+++ b/src/main.c
@@ -25,6 +25,9 @@
 #define DISP_STATUS  *((vu32*)(MEM_IO + 0x0004))
 #define DISP_VCOUNT  *((vu32*)(MEM_IO + 0x0006))
 
+// Bits for display control.
+#define DISP_CONTROL_PAGE (1 << 4)
+
 // Display modes.
 #define DISP_MODE_0 0x0000
 #define DISP_MODE_1 0x0001
@@ -40,11 +43,6 @@
 #define DISP_BG3 0x0800
 #define DISP_OBJ 0x1000
 
-static inline void
-set_display_mode(u16 value) {
-    *((vu32*)(MEM_IO + 0x0000)) = value;
-}
-
 // Screen settings.
 #define SCREEN_WIDTH 240
 #define SCREEN_HEIGHT 160
@@ -236,9 +234,9 @@ wait_vsync() {
 // memory, instead we need to read a u16 word, mask and or the corresponding
 // bits and wave the updated u16.
 static inline void
-put_pixel_m4(int x, int y, u8 col_index) {
+put_pixel_m4(int x, int y, u8 col_index, u16 *buffer) {
     int buffer_index = (y * SCREEN_WIDTH + x) / 2;
-    u16 *destination = &SCREEN_BUFFER[buffer_index];
+    u16 *destination = &buffer[buffer_index];
     // Odd pixels will go to the top 8 bits of the destination. Even pixels to
     // the lower 8 bits.
     int odd = x & 0x1;
@@ -250,24 +248,41 @@ put_pixel_m4(int x, int y, u8 col_index) {
 }
 
 static inline void
-draw_fill_rect_m4(int x0, int y0, int x1, int y1, u8 col_index) {
+draw_fill_rect_m4(int x0, int y0, int x1, int y1, u8 col_index, u16 *buffer) {
     int ix, iy;
     for(iy = y0; iy < y1; iy++) {
         for(ix = x0; ix < x1; ix++) {
-            put_pixel_m4(ix, iy, col_index);
+            put_pixel_m4(ix, iy, col_index, buffer);
         }
     }
 }
 
+static inline u16
+flip_page() {
+    DISP_CONTROL ^= DISP_CONTROL_PAGE;
+}
+
+#define SCREEN_PAGE_1 ((vu16*) MEM_VRAM)
+#define SCREEN_PAGE_2 ((vu16*) (MEM_VRAM + 0xa000))
+
 int main(void) {
-    set_display_mode(DISP_MODE_4 | DISP_BG2);
+    DISP_CONTROL = DISP_MODE_4 | DISP_BG2;
 
     PAL_BUFFER[1] = COLOR_RED;
     PAL_BUFFER[2] = COLOR_BLUE;
-    draw_fill_rect_m4(0, 0, 20, 20, 1);
 
+    // Prepare the screen buffers by drawing a rectangle with different colors
+    // to each page.
+    draw_fill_rect_m4(0, 0, 20, 20, 1, SCREEN_PAGE_1);
+    draw_fill_rect_m4(0, 0, 20, 20, 2, SCREEN_PAGE_2);
+
+    int frame_counter = 0;
     while(true) {
         wait_vsync();
+        if (frame_counter++ > 30) {
+            frame_counter = 0;
+            flip_page();
+        }
     };
 
     return 0;
-- 
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