Change how random data is generated

src/game_graphics.c

@@ -22,8 +22,8 @@
 #define TOP_OFFSET 7
 #define LEFT_OFFSET_B 1 // Left is offset by 1 bytes (7 pixels)
 
-static uint8_t *front_buf = (uint8_t*)DISPLAY_PAGE_1;
-static uint8_t *back_buf = (uint8_t*)DISPLAY_PAGE_2;
+static uint8_t *front_buf;
+static uint8_t *back_buf;
 
 #define BOX_CONTENT_SIZE 544
 
@@ -171,7 +171,7 @@ void draw_tiles(void) {
 #define ENDGAME_BOX_Y_OFFSET 16
 void ddraw_endgame_box(int8_t done, uint16_t score, uint16_t hi_score) {
 	// Clear the part of the screen where we'll draw
-	clear_box(SCREEN_WIDTH_B - (ENDGAME_BOX_X_OFFSET * 2), SCREEN_HEIGHT - (ENDGAME_BOX_Y_OFFSET * 2), ENDGAME_BOX_X_OFFSET, ENDGAME_BOX_Y_OFFSET, front_buf);
+	clear_box((SCREEN_WIDTH_B - (ENDGAME_BOX_X_OFFSET * 2)) + 1, (SCREEN_HEIGHT - (ENDGAME_BOX_Y_OFFSET * 2)) + CHAR_HEIGHT, ENDGAME_BOX_X_OFFSET, ENDGAME_BOX_Y_OFFSET, front_buf);
 	
 	// Horizontal lines
 	for(uint8_t row = 0; row < CHAR_HEIGHT; row++) {
@@ -248,6 +248,18 @@ void swap_display_buffers(void) {
 	PEEK(((uint16_t)front_buf == DISPLAY_PAGE_1) ? IO_DISPLAY_PAGE1 : IO_DISPLAY_PAGE2);
 }
 
+void clear_display_buffers(void) {
+	// Clear the buffers
+	memset((void*)DISPLAY_PAGE_1, 0, DISPLAY_PAGE_SIZE);
+	memset((void*)DISPLAY_PAGE_2, 0, DISPLAY_PAGE_SIZE);
+	
+	PEEK(IO_DISPLAY_PAGE1); // Select the first display page
+	
+	// Restore the buffer ordering
+	front_buf = (uint8_t*)DISPLAY_PAGE_1;
+	back_buf = (uint8_t*)DISPLAY_PAGE_2;
+}
+
 void draw_field_borders_on_buffer(uint8_t brd, uint8_t* buf) {
 	// Horizontal borders
 	for(uint8_t col = 0; col < (GRID_SIDE * (GRID_CELL_SIDE/7)) + 1; col++) {

src/game_graphics.h

@@ -26,6 +26,7 @@ void draw_number(uint16_t n, uint8_t len, uint8_t x, uint8_t y);
 void draw_tiles(void);
 void ddraw_single_tile(uint8_t offset);
 void swap_display_buffers(void);
+void clear_display_buffers(void);
 void clear_box(uint8_t w, uint8_t h, uint8_t off_x, uint8_t off_y, uint8_t *disp_buf);
 void ddraw_direction_arrows(arrow_direction dir);
 void ddraw_endgame_box(int8_t done, uint16_t score, uint16_t hi_score);

src/game_logic.c

@@ -40,13 +40,21 @@ uint8_t *get_front_grid(void) {
 uint8_t add_random_tile(void) {
 	uint16_t rand = lfsr_update();
 	uint8_t tile_val = (rand & 0x000F) > 0x0D ? 2 : 1; // ~90% chance of a tile of type 1 (a "2"), 10% of a type 2 (a "4")
-	uint8_t rand_offset = rand >> 8;
+	
+	uint8_t free_tiles = 0;
+	uint8_t chosen_tile;
 	
 	for (uint8_t offset = 0; offset < GRID_SIDE * GRID_SIDE; offset++) {
-		uint8_t rand_off = (offset + rand_offset)%(GRID_SIDE * GRID_SIDE);
-		if (!front_grid[rand_off]) {
-			front_grid[rand_off] = tile_val;
-			return rand_off + 1;
+		if (!front_grid[offset]) free_tiles++;
+	}
+	
+	if(!free_tiles) return 0;
+	chosen_tile = (rand >> 8) % free_tiles;
+	
+	for (uint8_t offset = 0; offset < GRID_SIDE * GRID_SIDE; offset++) {
+		if (!front_grid[offset] && !(chosen_tile--)) {
+			front_grid[offset] = tile_val;
+			return offset + 1;
 		}
 	}
 	

src/main.c

@@ -25,7 +25,6 @@
 #define WIN_SCORE_BONUS 10000
 
 void init(void);
-void clear_display(void);
 
 // Low level initialization
 void init(void) {
@@ -33,15 +32,9 @@ void init(void) {
 	PEEK(IO_ROMSEL); // Make sure the ROM is selected
 	
 	PEEK(IO_DISPLAY_BW); // Disable colors
-	PEEK(IO_DISPLAY_PAGE1); // Select the first display page
 	
 	// Clear display memory
-	clear_display();
-}
-
-void clear_display(void) {
-	memset((void*)DISPLAY_PAGE_1, 0, DISPLAY_PAGE_SIZE);
-	memset((void*)DISPLAY_PAGE_2, 0, DISPLAY_PAGE_SIZE);
+	clear_display_buffers();
 }
 
 __task int main(void) {
@@ -65,7 +58,7 @@ __task int main(void) {
 			lfsr_update();
 		}
 		BELL1();
-		clear_display(); // Clear display again
+		clear_display_buffers(); // Clear display again
 	
 		// Reset the game, calculate the initial score depending on which tiles we randomly get
 		score = reset_game();