A Polygon Sprite is also a
Sprite, that is used to display a 2d image.
However, unlike a normal
Sprite object, which is a rectangle made of just 2
PolygonSprite objects are made of a series of triangles.
Why use a Polygon Sprite?
There is a lot of technical jargon that we can toss around here about pixel fill rate
but the take home lesson is that a
PolygonSprite draws based upon the shape of
Sprite, not a simple rectangle around the largest width and height. This
saves a lot of unnecessary drawing. Consider this example:
Notice the difference between the left and right versions?
On the left, a typical
Sprite drawn in rectangular fashion by the use of 2
On the right, a
PolygonSprite drawn with many smaller triangles.
Whether or not this trade-off is worth it for purely performance reasons depends on a number of factors (sprite shape/detail, size, quantity drawn on screen, etc.), but in general, vertices are cheaper than pixels on modern GPUs.
AutoPolygon is a helper class. It's purpose is to process an image into a 2d
polygon mesh at runtime.
There are functions for each step in the process, from tracing all the points,
to triangulation. The result, can be then passed to a
Sprite objects create
function to create a
// Generate polygon info automatically. auto pinfo = AutoPolygon::generatePolygon("filename.png"); // Create a sprite with polygon info. auto sprite = Sprite::create(pinfo);