dangerzone/src/engine/engine.c

#include "engine.h"

engine_internal_state_t *internal_state = NULL;
game_state_t *game_state = NULL;

void
mark_dirty_rect(int x, int y, int w, int h)
{
    if (w <= 0 || h <= 0) {
        return;
    }

    // clip rectangle to the framebuffer
    if (x < 0) {
        w += x;
        x = 0;
    }

    if (y < 0) {
        h += y;
        y = 0;
    }

    if (x + w > game_state->width) {
        w = game_state->width - x;
    }

    if (y + h > game_state->height) {
        h = game_state->height - y;
    }

    if (w <= 0 || h <= 0) {
        return;
    }

    SDL_Rect rect = {
        .x = x,
        .y = y,
        .w = w,
        .h = h
    };

    if (!game_state->framebuffer_dirty) {
        game_state->dirty_rect = rect;
        game_state->framebuffer_dirty = true;
        return;
    }

    int left = game_state->dirty_rect.x < rect.x
        ? game_state->dirty_rect.x
        : rect.x;

    int top = game_state->dirty_rect.y < rect.y
        ? game_state->dirty_rect.y
        : rect.y;

    int old_right =
        game_state->dirty_rect.x + game_state->dirty_rect.w;

    int new_right = rect.x + rect.w;

    int old_bottom =
        game_state->dirty_rect.y + game_state->dirty_rect.h;

    int new_bottom = rect.y + rect.h;

    int right = old_right > new_right
        ? old_right
        : new_right;

    int bottom = old_bottom > new_bottom
        ? old_bottom
        : new_bottom;

    game_state->dirty_rect = (SDL_Rect) {
        .x = left,
        .y = top,
        .w = right - left,
        .h = bottom - top
    };
}

bool
upload_dirty_texture(void)
{
    if (!game_state->framebuffer_dirty) {
        return true;
    }

    SDL_Texture *texture =
        internal_state->sdl_state->texture;

    SDL_Rect rect = game_state->dirty_rect;

    void *locked_pixels = NULL;
    int locked_pitch = 0;

    if (!SDL_LockTexture(
            texture,
            &rect,
            &locked_pixels,
            &locked_pitch
        )) {
        SDL_Log(
            "SDL_LockTexture failed: %s",
            SDL_GetError()
        );
        return false;
    }

    const size_t source_pitch =
        (size_t)game_state->width * sizeof(uint32_t);

    const size_t row_bytes =
        (size_t)rect.w * sizeof(uint32_t);

    const uint8_t *source =
        (const uint8_t *)game_state->framebuffer +
        (size_t)rect.y * source_pitch +
        (size_t)rect.x * sizeof(uint32_t);

    uint8_t *destination =
        (uint8_t *)locked_pixels;

    for (int y = 0; y < rect.h; ++y) {
        memcpy(
            destination + (size_t)y * locked_pitch,
            source + (size_t)y * source_pitch,
            row_bytes
        );
    }

    SDL_UnlockTexture(texture);

    game_state->framebuffer_dirty = false;

    return true;
}

void
engine_start() {
	// main game loop
	while(game_state->is_running) {
		// poll events
		while (SDL_PollEvent(&game_state->event)) {
			internal_state->engine_poll_events();
		}

		// call the user-defined framebuffer manipulation function
		internal_state->engine_update_framebuffer();

		// update the texture with the modified framebuffer
		upload_dirty_texture();

		SDL_RenderClear(
			internal_state->sdl_state->renderer
		);

		SDL_RenderTexture(
			internal_state->sdl_state->renderer, 
			internal_state->sdl_state->texture, 
			NULL, NULL
		);
		
		SDL_RenderPresent(
			internal_state->sdl_state->renderer
		);
	}
}

void
engine_stop() {
	engine_sdl_destroy(internal_state->sdl_state);
	free(internal_state);
	free(game_state);
}