arcade.TextureAtlas is where your textures eventually end up
when they are used in a sprite. This is where the image data is moved
to graphics memory (OpenGL) and is one of the reasons we can
batch draw hundreds of thousands of sprites extremely fast.
A texture atlas is basically a large texture containing multiple textures and we keep track of where these textures are located. Arcade’s texture atlas reside in graphics memory and is dynamic meaning textures can be added and removed on the fly.
Arcade’s texture atlas also automatically resize when needed all the way up to the maximum texture size your hardware supports. This requires a complete rebuild of the atlas, something we do on the gpu itself to minimize the impact of this operations. For average hardware it’s something you won’t notice runtime.
It’s also important to note that texture atlases can only be created after the window has been crated. Textures and sprites can be created before the window because they don’t interact with OpenGL directly. This part is usually the most time consuming while atlases are very fast to create and build.
Currently we use a very simple row based allocation algorithm to make room for new textures over time. This means that very tall textures can end up taking a lot of vertical space.
The maximum size of the atlas is usually 16384 x 16384 if we are targeting average hardware.
Atlases will resize automatically when full. It will also try to pack the textures better by sorting them by their height.
Default Texture Atlas
Most users will not be aware that arcade is using a texture atlas under the hood. More advanced users can take advantage of these if they run into limitations.
Arcade has a global default texture atlas stored in
This is an instance of
arcade.ArcadeContext where the low
level rendering api is accessed (OpenGL).
Instead of relying on the global texture atlas we can also create our own.
Sprite lists take an
atlas argument for supplying your own texture atlas instance.
This atlas can also be shared between several sprite lists if needed.
# Create an empty 256 x 256 texture atlas my_atlas = TextureAtlas((256, 256)) spritelist = SpriteList(atlas=my_atlas)
When new textures are detected (sprite is added to list) the texture is added to the atlas.
We can also pre-add textures into an atlas before the game starts to avoid potential minor stalls. This is usually not a problem, but when adding a large amount of them it can be noticeable.
# List of arcade.Texture instances list_of_textures = ... # Create an atlas with a reasonable size for a list of textures atlas = TextureAtlas.create_from_texture_sequence(list_of_textures) # Create an atlas with a specific size and initial textures atlas = TextureAtlas((256, 256), textures=list_of_textures) # We can also pre-add textures at any time using: # (can also be done with the default texture atlas) atlas.add(texture)
Atlases has a
border property that is
1 by default. This is important
to avoid “texture bleeding” between borders of the textures in the atlas.
This is a very common issues in games using the gpu based graphics and is
even a problem with using
NEAREST interpolation when sprites are rotating.
Keep the default value of this property unless you know exactly what you are doing.
In some instances it can be useful to update a texture. We would normally
do this by modifying the Pillow texture in the
instance. However, this doesn’t update the texture in the atlas itself.
We can manually update it:
# Change the internal image in a texture texture.image # <- Modify or crate a new image with the same size # Write the new image data to the atlas atlas.update_texture_image(texture)
This updates the already allocated region and the image needs to be exactly the same size. This should be used sparingly or at least not a per frame operation. If can be fast as a per-frame operation, but you’ll need to profile that. Animated sprites are much better option, but of course requires pre-determined texture frames.
If you have stale textures they can be removed from the atlas using:
This will make the region free for new textures the next time the
atlas rebuilds. You can also call
directly if you are removing a large quantity of textures, but generally
it’s enough to let this happen automatically when needed.
Rendering Into Atlas
A much faster way to update a texture in the atlas is rendering directly into it. This can for example be used to make a minimap for your game or in any case you need the sprite texture to be really dynamic (not decided by pre-made texture frames). It can be used in many creative ways.
# --- Initialization --- # Create an empty texture so we can allocate some space in the atlas texture = arcade.Texture.create_empty("render_area_1", size=(256, 256)) # Assign the texture to a sprite sprite = arcade.Sprite(center_x=200, center_y=300, texture=texture) # Create the spritelist and add the sprite spritelist = arcade.SpriteList() # Adding the sprite will also add the texture to the atlas spritelist.append(sprite) # -- Rendering --- # Let's render something into our texture directly. # All operations will only affect the allocated portion of the atlas for texture. # We are given a framebuffer instance representing this area with spritelist.atlas.render_into(texture) as framebuffer: # Clear the allocated region in the atlas (if you need it) framebuffer.clear() # From here on we can draw using any arcade draw functionality arcade.draw_rectangle_filled(128, 128, 160, 160, arcade.color.WHITE, rotation) # Draw the spritelist and see your animating sprite texture spritelist.draw()
Doing the rendering part above every frame (and incrementing
rotation by delta time)
will give you a sprite with a rotating rectangle a a texture. Again, you can draw anything
into this texture area. Spritelists, shapes and whatnot.
We can also specify what should be projected into this texture area in the atlas.
By default the projection will be
(0, width, 0, height), but this is not always
what you want (were
height are the region/texture size)
# Assuming your window is 800 x 600 we could draw the entire game into this atlas region projection = 0, 800, 0, 600 with spritelist.atlas.render_into(texture, projection=projection) as framebuffer: framebuffer.clear() # Draw your game here # Draw sprite with a texture containing your entire game here
Scrolling can also be applied to projection just like cameras.
# Scroll projection (or even zoom) projection = 0 + scroll_x, 800 + scroll_x, 0 + scroll_y, 600 + scroll_y
Rendering into an atlas is superior (at least 100 times faster) to updating texture data using Pillow, but that doesn’t mean it’s free. We can possibly get away with 50-100 of these per frame, but this is something you will have to profile.
When working with atlases it can be useful to see the contents. We provide two methods for this.
arcade.TextureAtlas.show() will display the atlas using Pillow:
arcade.TextureAtlas.save() will save the atlas contents to a png file:
Both of these methods will “download” the atlas texture from graphics memory for you to inspect the raw data.