rework random shape selection

src/game/game.c

@@ -13,9 +13,24 @@
 #include "tetromino/placing.h"
 
 
-void set_next_shape(GameData* const game_data) {
-    ShapeId id = (rand() % TETROMINO_COUNT) | (rand() % 4 << 3);
-    game_data->next_shape = id;
+void next_shape(GameData* const game_data) {
+    game_data->curr_idx++;                            // increase the current shape index
+    game_data->sel_x = COLUMNS / 2 - SHAPE_WIDTH / 2; // move the shape position to the centre
+    game_data->sel_y = 0;
+
+    // return if know which shape is next
+    if (game_data->curr_idx < (TETROMINO_COUNT - 1))
+        return;
+
+    game_data->curr_idx = 0;
+
+    // shuffle the next shapes using a Fisher–Yates shuffle
+    for (uint8_t i = 0; i < (TETROMINO_COUNT - 1); i++) {
+        const uint8_t j = i + rand() % (TETROMINO_COUNT - i);
+        const ShapeId cache = game_data->nxt[i];
+        game_data->nxt[i] = game_data->nxt[j];
+        game_data->nxt[j] = cache;
+    }
 }
 
 void game_init(GameData* const game_data) {
@@ -31,9 +46,12 @@ void game_init(GameData* const game_data) {
     // set a random seed using the system clock
     srand(time(NULL));
 
-    set_next_shape(game_data);
-    game_data->selected = (SelectedShape){game_data->next_shape, COLUMNS / 2 - SHAPE_WIDTH / 2, 0};
-    set_next_shape(game_data);
+    // set the shape data in each slot to it's corrsponding ID
+    for (ShapeId i = 0; i < TETROMINO_COUNT; i++)
+        game_data->nxt[i] = i;
+
+    game_data->curr_idx = ~1; // set the current index to the max (well, so it becomes the max after increment)
+    next_shape(game_data);    // select the next shape (a refresh is triggered due to the current index being too high)
 }
 
 // called every time the game's state is updated

src/game/game.h

@@ -9,22 +9,18 @@
 #define COLUMNS ((int8_t)10)
 #define ROWS    ((int8_t)(COLUMNS * 2))
 
-typedef struct {
-    ShapeId id;
-    int8_t x;
-    int8_t y;
-} SelectedShape;
-
 typedef const Colour* CRow;
 typedef Colour* Row;
 
 typedef struct {
     Row rows[ROWS];
-    SelectedShape selected;
-    ShapeId next_shape;
+    ShapeId nxt[7];   // the order of the shape ids that they should appear in
+    uint8_t curr_idx; // current shape index
+    int8_t sel_x;     // selected shape x position
+    int8_t sel_y;     // selected shape y position
 } GameData;
 
-void set_next_shape(GameData* game_data);
+void next_shape(GameData* game_data);
 void game_init(GameData* game_data);                        // initializes the game
 void game_update(GameData* game_data, const uint8_t* keys); // updates the game's state
 void game_free(GameData* game_data);                        // free all data stored with the game

src/game/tetromino/placing.c

@@ -97,36 +97,39 @@ static inline ShapeId rotate_id(const ShapeId id, const int dir) {
 }
 
 void place_update(GameData* const game_data, const InputData move) {
-    SelectedShape* const selected = &game_data->selected;
+    // store the current index, only changes when placed (which yields no movement) and rotation (which occurs last)
+    ShapeId const curr_idx = game_data->curr_idx;
+
     // set the shape if we moved vertically and intersected
     if (move & 4) {
-        const int8_t y = selected->y + 1;
-        if (shape_intersects(game_data->rows, selected->id, selected->x, y)) {
-            set_shape(game_data->rows, selected->id, selected->x, selected->y); // if the shape intersects vertically, write the shape at the current position and return
+        const int8_t y = game_data->sel_y + 1;
+        if (shape_intersects(game_data->rows, game_data->nxt[curr_idx], game_data->sel_x, y)) {
+            set_shape(game_data->rows, game_data->nxt[curr_idx], game_data->sel_x, game_data->sel_y); // if the shape intersects vertically, write the shape at the current position and return
             clear_rows(game_data->rows);                                                              // clear the rows that have been completed
 
-            game_data->selected = (SelectedShape){game_data->next_shape, COLUMNS / 2 - SHAPE_WIDTH / 2, 0};
-            set_next_shape(game_data);
+            next_shape(game_data);
             return;
         }
 
         // otherwise, just set Y
-        selected->y = y;
+        game_data->sel_y = y;
     }
 
     // update shape's X coordinate movement
     if ((move & 3) != 3 && (move & 3)) {
-        const int8_t x = selected->x + ((move & 3) == 1 ? -1 : 1); // either move along -x or +x
-        if (shape_intersects(game_data->rows, selected->id, x, selected->y) == false) {
-            selected->x = x; // set X if the shape does not intersect
+        const int8_t x = game_data->sel_x + ((move & 3) == 1 ? -1 : 1); // either move along -x or +x
+        if (shape_intersects(game_data->rows, game_data->nxt[curr_idx], x, game_data->sel_y) == false) {
+            game_data->sel_x = x; // set X if the shape does not intersect
         }
     }
 
     // update the shape's rotation
     if (move & 8 || move & 16) {
-        const ShapeId id = move & 8 ? rotate_id(selected->id, -8) : rotate_id(selected->id, 8);
-        if (shape_intersects(game_data->rows, id, selected->x, selected->y) == false) {
-            selected->id = id;
+        const ShapeId id = move & 8 // check which direction we should move
+                               ? rotate_id(game_data->nxt[curr_idx], -8)
+                               : rotate_id(game_data->nxt[curr_idx], 8);
+        if (shape_intersects(game_data->rows, id, game_data->sel_x, game_data->sel_y) == false) {
+            game_data->nxt[curr_idx] = id;
         }
     }
 }

src/window/renderer.c

@@ -44,19 +44,20 @@ static inline void set_colour(SDL_Renderer* renderer, Colour c) {
 }
 
 // draw the selected block
-static void render_selected(SDL_Renderer* renderer, SelectedShape selected) {
-    Shape selected_shape = shape_from_id(selected.id);
-    set_colour(renderer, colour_from_id(selected.id));
+static void render_selected(SDL_Renderer* renderer, GameData* const game_data) {
+    const ShapeId id = game_data->nxt[game_data->curr_idx];
+    const Shape shape = shape_from_id(id);
+    set_colour(renderer, colour_from_id(id));
 
     for (int8_t y = 0; y < SHAPE_HEIGHT; y++) {
-        ShapeRow shape_row = shape_get_row(selected_shape, y);
+        const ShapeRow shape_row = shape_get_row(shape, y);
 
         if (shape_row == 0)
             continue;
 
         for (int8_t x = 0; x < SHAPE_WIDTH; x++)
             if (is_set(shape_row, x))
-                draw_block(renderer, selected.x + x, selected.y + y);
+                draw_block(renderer, game_data->sel_x + x, game_data->sel_y + y);
     }
 }
 
@@ -83,7 +84,7 @@ void renderer_update(const RenderData* render_data) {
     success |= SDL_SetRenderDrawColor(renderer, 0x00, 0x00, 0x00, 0xFF);
     success |= SDL_RenderClear(renderer);
 
-    render_selected(renderer, render_data->game_data->selected);
+    render_selected(renderer, render_data->game_data);
     render_level(renderer, render_data->game_data);
 
     if (success < 0) {