Fractalis zooming

zoom.c

static void do_zoom(AppState* app, tina* coro, int button, double direction){
	if(glfwGetMouseButton(app->window, button) != GLFW_PRESS) return;

	Camera* cam = &app->camera;
	double speed = 0;
	double t0 = glfwGetTime();
	while(glfwGetMouseButton(app->window, button) == GLFW_PRESS){
		double t1 = glfwGetTime();
		double dt = t1 - t0;
		t0 = t1;
		
		speed = fmin(speed + 3*dt, 3);
		double zoom = exp(direction*speed*dt);
		vec2 mouse; glfwGetCursorPos(app->window, &mouse.x, &mouse.y);
		vec2 pivot = affine_point(input_transform(app), mouse);
		Affine t = {1, 0, 0, 1, -pivot.x, -pivot.y};
		t = affine_mul((Affine){zoom, 0, 0, zoom, pivot.x, pivot.y}, t);
		
		Camera cam = app->camera;
		app->camera.a = cam.a*t.a + cam.c*t.b;
		app->camera.b = cam.b*t.a + cam.d*t.b;
		app->camera.c = cam.a*t.c + cam.c*t.d;
		app->camera.d = cam.b*t.c + cam.d*t.d;
		app->camera.x = fx_add(&app->camera.x, (fx[]){d_to_fx(cam.a*t.x + cam.c*t.y)});
		app->camera.y = fx_add(&app->camera.y, (fx[]){d_to_fx(cam.b*t.x + cam.d*t.y)});
		
		double scale = (hypot(cam.a, cam.b) + hypot(cam.c, cam.d))/TILE_SIZE;
		printf("scale: %e\n", scale);
		
		app->dirty = true;
		tina_yield(coro, 0);
	}
}