After playing Environmental Station Alpha, I decided I wanted to implement the screen tearing effect Hempuli is using in his game. I didn’t know how he achieved it so I had to start from scratch and think about different approaches.
Knowing nothing about shaders, I was left with surfaces. I jotted down some code and immediately hit a wall; after asking around in the yoyogames forums, reading other’s comments, I could finally come up with a pretty decent solution.
Actual Code
I wrote the code so it could be easily hackable. This goes into the create event of your game controller object.
// handy shorter names dw = display_get_width() dh = display_get_height() tearings_surface = surface_create(dw, dh) // We'll draw on this surface tearings_y = 0 band_num = 16 // How many bands you want on screen band_height = dh / band_num tearings_x_offset = 32 // How much you want to displace the bands horizontally tearing_speed = 4 // Change this to speed up/slow down the tearings
I place the following code inside a draw_post event of my controller.
// Create surface if it doesn't exits
if !surface_exists(tearings_surface)
tearings_surface = surface_create(display_get_width(), display_get_height())
// Let's set the target to our surface
surface_set_target(tearings_surface)
draw_clear_alpha(c_black, 0)
// We draw parts of our application surface on tearings surface
for (var current_band = 0; current_band < band_num * 2; current_band++)
{
draw_surface_part(application_surface, 0, band_height * current_band - tearings_y, dw, band_height, sin( (degtorad(360) / band_num ) * current_band) * tearings_x_offset , band_height * current_band - tearings_y)
}
// Always reset the target surface
surface_reset_target()
// Draw the actual surface
draw_surface_stretched(tearings_surface, -tearings_x_offset, 0, dw + tearings_x_offset * 2, dh)
// Move the Tearings
tearings_y = (tearings_y + tearing_speed) % (band_height * band_num)
That's it.
And this is how I make that effect. I will implement a similar version for vertical tearings (for underwater levels? maybe?). Hope you find it useful.
A note about surfaces: remember to free the surfaces if you don’t need them anymore, otherwise it will lead to memory leaks.