Previously, we would just stuff the entire tilemap vertex data
four times into the buffers, with only the autotile vertices
offset according to the animation frame. This meant we could
prepare the buffers once, and then just bind a different offset
for each animation frame without any shader changes, but it also
lead to a huge amount of data being duplicated (and blowing up
the buffer sizes).
The new method only requires one buffer, and instead animates by
recognizing vertices belonging to autotiles in a custom vertex
shader, which offsets them on the fly according to the animation
index.
With giant tilemaps, this method would turn out to be a little
less efficient, but considering the Tilemap is planned to be
rewritten to only hold the range of tiles visible on the screen
in its buffers, the on the fly offsetting will become neglient,
while at the same time the amount of data we have to send to the
GPU everytime the tilemap is updated is greatly reduced; so a
net win in the end.
This implementation is also heaps better than the old
one as it doesn't use a (differently sized) aux texture,
meaning the Bitmap discards its old texture and aquires
one of same size, making reuse through the TexPool a
lot more likely. It also saves on the aux texture blits
and binding switches.
As the setup / resource acquisition far outweighs the
actual rendering cost, operation time is relatively
constant no matter how many divisions are used.
The drawing is now completely shader based, which makes away
with all usage of the depracted matrix stack. This also allows
us to do things like simple translations and texture coordinate
translation directly instead of doing everything indirectly
through matrices.
Fixed vertex attributes ('vertexPointer()' etc) are also
replaced with user defined attribute arrays.
Jonas Kulla
Edward Rudd