samples / sprite.c

In this example we create a wizard sprite and a walk cycle animation. We then animate the sprite and draw it on screen.

#include "cage.h"

The sprite struct

This is our wizard struct. It holds the wizard sprite resource and the walk cycle animation resource. In this sample, we use a static variable instead of dynamically allocating an instance.

static struct wizard {
    struct sprite* sprite;
    struct animation* walk_cycle;
} wizard = { NULL, NULL };
static void* create_sample(void);
static void destroy_sample(void* data);

Prepare the sprite

We use the game state create() function to create the sprite using an image resource, as well as the animation resource for the walk cycle. If no errors are encountered, we proceed to add frames to the walk cycle animation. Finally, we play the animation, making it active for the sprite. Notice the way we use a static variable to hold the wizard struct and use its pointer as the create() function return value.

static void* create_sample(void)
    wizard.sprite = create_sprite(create_image("res/wizard.png"), 32, 32);
    if (wizard.sprite == NULL) goto error;
    wizard.walk_cycle = create_animation();
    if (wizard.walk_cycle == NULL)
        goto error;
    else {
        struct frame frames[] = { { 0, 300, NULL },
                                  { 1, 300, NULL },
                                  { 2, 300, NULL },
                                  { 3, 300, NULL } };
        add_frames(wizard.walk_cycle, 4, frames);
        wizard.walk_cycle->loop_from = 0;
        wizard.walk_cycle->loop_to = 3;
    play_animation(wizard.sprite, wizard.walk_cycle);
    return &wizard;
    return NULL;

Animate & draw

During the game, the update function uses the wizard data to animate and draw the sprite. The elapsed_ms argument is used by the animate_sprite() function so it can track how long to play each animation frame.

static void update_sample(void* data, float elapsed_ms)
    struct wizard* w = data;
    animate_sprite(w->sprite, elapsed_ms);
    draw_sprite(w->sprite, 10, 10);


Before exiting a state (or the game), Cage will call the destroy function. Having allocated 3 resources earlier in the create function, now is the time to clean up by matching each create with a destory call.

static void destroy_sample(void* data)
    struct wizard* w = data;


Finally, the game’s main function delegates the execution to the game_loop() function together with the 3 state functions we wrote.

int main(void)
    return game_loop(create_sample, update_sample, destroy_sample);