From 3d38da89150835237767047c2fb9555ec306be49 Mon Sep 17 00:00:00 2001
From: hkz <tabaglio@posteo.net>
Date: Wed, 16 Jul 2025 14:24:57 +0200
Subject: [PATCH] Add base game logic

---
 src/game_logic.c | 75 ++++++++++++++++++++++++++++++++++++++++++++++--
 src/game_logic.h |  5 ++--
 2 files changed, 74 insertions(+), 6 deletions(-)

diff --git a/src/game_logic.c b/src/game_logic.c
index 8bf9235..0a2faf0 100644
--- a/src/game_logic.c
+++ b/src/game_logic.c
@@ -1,7 +1,9 @@
 #include "game_logic.h"
 
-static uint8_t game_grid_alpha[GRID_WIDTH * GRID_HEIGHT];
-static uint8_t game_grid_beta[GRID_WIDTH * GRID_HEIGHT];
+#include <string.h>
+
+static uint8_t game_grid_alpha[GRID_SIDE * GRID_SIDE];
+static uint8_t game_grid_beta[GRID_SIDE * GRID_SIDE];
 
 static uint8_t *front_grid = game_grid_alpha;
 static uint8_t *back_grid = game_grid_beta;
@@ -15,13 +17,80 @@ void swap_grids(void) {
 	back_grid = temp;
 }
 
-uint8_t *get_current_grid(void) {
+uint8_t *get_front_grid(void) {
 	return front_grid;
 }
 
 uint8_t *step_game(step_direction dir) {
 	// TODO: Update the grid state calculating the new state in the back grid
 	
+	uint8_t start_offset;
+	int8_t column_step;
+	int8_t row_step;
+	
+	/*
+	 *	UP: scans TOP to BOTTOM, RIGHT to LEFT
+	 *	DOWN: scans BOTTOM to TOP, RIGHT to LEFT
+	 *	LEFT: scans LEFT to RIGHT, TOP to BOTTOM
+	 *	RIGHT: scans RIGHT to LEFT, TOP to BOTTOM
+	 */
+	
+	switch(dir) {
+		case UP:
+			start_offset = GRID_SIDE;
+			column_step = GRID_SIDE;
+			row_step = -1;
+			break;
+		case DOWN:
+			start_offset = (GRID_SIDE * GRID_SIDE) - 1;
+			column_step = -GRID_SIDE;
+			row_step = -1;
+			break;
+		case LEFT:
+			start_offset = 0;
+			column_step = 1;
+			row_step = GRID_SIDE;
+			break;
+			break;
+		case RIGHT:
+			start_offset = GRID_SIDE - 1;
+			column_step = -1;
+			row_step = GRID_SIDE;
+			break;
+	};
+	
+	// Clear the back grid
+	memset(back_grid, 0, GRID_SIDE * GRID_SIDE);
+	
+	for (int8_t row = 0; row < GRID_SIDE; row++) {
+		for(int8_t col = 0; col < GRID_SIDE; col++) {
+			uint8_t current_offset = start_offset + (col * column_step) + (row * row_step);
+			uint8_t sub_col;
+			
+			// Search for the first non-zero value in the front grid and copy it in the current place of the back grid (zeroing it in the front)
+			for(sub_col = col; sub_col < GRID_SIDE; sub_col++) {
+				uint8_t sub_col_offset = start_offset + (sub_col * column_step) + (row * row_step);
+				if(front_grid[sub_col_offset]) {
+					back_grid[current_offset] = front_grid[sub_col_offset];
+					front_grid[sub_col_offset] = 0;
+					break;
+				}
+			}
+			
+			// The value is still 0, we found nothing. On to the next row!
+			if (!back_grid[current_offset]) break;
+			
+			// Now search if there is an identical value following this one, so we can merge them
+			for(; sub_col < GRID_SIDE; sub_col++) {
+				uint8_t sub_col_offset = start_offset + (sub_col * column_step) + (row * row_step);
+				if(front_grid[sub_col_offset] == back_grid[current_offset]) {
+					back_grid[current_offset]++; // Merge them (by increasing the value of the current square and removing the merged one)
+					front_grid[sub_col_offset] = 0;
+					break;
+				}
+			}
+		}
+	}
 	
 	swap_grids();
 	
diff --git a/src/game_logic.h b/src/game_logic.h
index 94057cb..fc9d6ac 100644
--- a/src/game_logic.h
+++ b/src/game_logic.h
@@ -3,8 +3,7 @@
 
 #include <stdint.h>
 
-#define GRID_WIDTH 5
-#define GRID_HEIGHT 5
+#define GRID_SIDE 5
 
 typedef enum {
 	UP,
@@ -13,7 +12,7 @@ typedef enum {
 	RIGHT
 } step_direction;
 
-uint8_t *get_current_grid(void);
+uint8_t *get_front_grid(void);
 uint8_t *step_game(step_direction dir);
 
 #endif /* _GAME_LOGIC_HEADER_ */