perf(webgl2): skip uniform updates when nothing changed (dirty flag)

[Endymi0n74]

What

WebGL2Player.updateCanvas() was issuing its 7 gl.uniform* calls on every refresh, even though all uniform inputs are constant unless the options change:

• the processing options (filterId, qualityMode, sharpenFactor, brightness, contrast, saturation) are only mutated through updateOptions(),
• the drawing-buffer size (iResolution ← $canvas.width/height) is fixed at construction.

A private _uniformsDirty flag (set by updateOptions() and refreshPlayer()) turns the steady 60 Hz path into 1 field read + 1 branch. Also removes a leftover debug console.log from the hot path.

Why

updateCanvas() runs at the render cadence. In the current TS source it also performs 7 gl.getUniformLocation() lookups per call — skipped entirely when nothing changed. The fork that this ports from measured the steady path at ~246 ns/frame → ~12.7 ns/frame (×19.4), with the earlier measurement including the uniform-location cache at ×22.

Safety

• The flag starts at true, so the initial uniforms are still applied in setupShaders() (which calls updateCanvas() once at init).
• Every mutation path invalidates the flag: updateOptions() (override of BaseStreamPlayer.updateOptions, same contract: Object.assign + optional refreshPlayer()) and refreshPlayer() (called by the stream manager on settings changes / player refresh).
• No behavior change when options actually change: the same 7 uniform values are written, just not redundantly.
• The uniform cache (comparing values to skip identical writes) is deliberately not part of this PR — one subject at a time.

Measurement

Steady-path updateCanvas (JS cost only, 60 Hz scenario, Node V8 harness, seeds 42/2024/999 × 3 passes × 200 000 iterations):

Build	ns/frame	Δ
before (7 uniforms per call)	~246	—
after (dirty flag)	~12.7	×19.4

Visual output unchanged: the same uniform values are written whenever anything changes.