The `isTouchingColor` function now takes an optional mask parameter. If
provided, only the parts of the Drawable which match the mask color will
be used for the test. For example:
```
isTouchingColor(4, red, blue);
```
This means "are there any parts of Drawable #4 which are blue and are
touching a red pixel on some other Drawable?"
HSL's lightness is, in this case, basically the same as half of HSV's
value, so this change halves the threshold value used by the color
effect to make it similar in appearance to the HSV implementation.
This will allow rendering the primary view, picking view, and "touching
color" view with different projection matrices without needing to
recalculate the model matrix for every Drawable every time.
Pixelate still needs a bit more work: at certain scales the edges of the
"pixels" are ragged. This happens in Scratch 2.0 as well, but for me it
seems slightly worse in this implementation.
The renderer now uses premultiplied alpha in the frame buffer, though
textures are still stored without premultiplied alpha. This makes it
easier to get the desired results from the browser's canvas compositing
step, and might be nicer for mobile hardware depending on which parts of
the Internet you believe.
This implementation of the pixel effect is now very similar to the
PixelBender implementation in Scratch 2.0
I also added a slider to demo.html as a debugging aid: it manipulates a
value that is passed into the shader and used in whatever way helps.
The current fragment chader contains non-uniform control flow for
determining the texture coordinates to use with `texture2D()`. The spec
says that this can cause undefined behavior; in my case I see a
"sparkle" of wrong pixels near primitive edges.
See:
https://www.opengl.org/wiki/Sampler_%28GLSL%29#Non-uniform_flow_control
This change introduces the Drawable class, which corresponds to a
Scratch sprite or clone. It supports setting its "skin" (corresponding
to a Scratch costume) by md5+extension, but currently only supports
bitmap skins. Drawables can be created, destroyed, and otherwise
manipulated by ID through the renderer.
