Make the text color a rendering variable, so that it can be passed
through as uniform to the glyph shader and applied to the gray
map of the glyphs. This avoids re-creating the glyph runs when
merely the color changes.
This already "worked" for the glyph cache based text rendering,
but it wasn't used because of the wasm canvas code path. This
patch changes that to render the text into a text using simply black
and then render that texture using our existing glyph shader,
which merely uses the alpha channel anyway.
This reduces also #cfg's.
The path shader uses only one attribute array, while the others use two.
First rendering with say the glyph shader and then the path one may leave
odd artifacts around with GLES, which is fixed by properly disabling the
vertex attribute arrays after use.
Closes: #17
We already keep the context in an RC, might as well keep another copy :-)
This re-applies commit 9b0dfa14b5 but
replaces the Clone trait on Shader, which would lead to duplicate and
too early program deletion, with an Rc<Shader>.
Based on Olivier's suggestion, the text rendering primitive is created
by painting the text onto a temporary HTML canvas
element and binding that to a texture.
The GL bindings were missing one feature on the web side, the ability to
set texture image data from an HTML canvas element.
We're going to need that soon.
The bump to a newer version also came with some odd (but sensible)
source incompatibilities.
