gui_toolkit 0.6.0

Added

• Blend spaces: render.Blend_Space (Linear, Srgb): where colors mix (blending, antialiased edges,
  interpolation, image filtering and mips, layer composites). Srgb composites like web browsers (CSS Color 4 /
  Compositing 1: rgba(0, 0, 0, .5) over white is 128). render.init(..., space), render.init_offscreen(..., space),
  render.set_blend_space (at run time: frame view, translucent swap chain format and color space, pooled targets),
  render.blend_space. Per layer: draw.Layer_Effects.space (draw.Layer_Space), draw.blend_space(dc);
  render.Layer.space, render.Image_Ref.space.
• draw.set_interpolation(dc, .Target | .Srgb | .Linear) (draw.Interpolation): where corner colors interpolate
  (render.FLAG_LERP_SRGB, FLAG_LERP_LINEAR), e.g. CSS gradients in sRGB whatever the frame's space.
• RGBA textures stored in the renderer's space when created (render.texture_space; R8G8B8A8_UNORM premultiplied on
  sRGB values in Srgb), converted by the shader when drawn into a target of the other space (render.FLAG_TEX_SRGB).
• Text correction: render.Text_Rendering (curve: None, Srgb, Power; gamma, contrast,
  coverage_exponent), render.set_text_rendering, render.text_rendering, render.text_rendering_default,
  TEXT_RENDERING_LINEAR (the historical look), TEXT_RENDERING_SRGB (Chromium on Windows: Skia's sRGB curve,
  contrast 1.0). Skia's SkMaskGamma computed per glyph in the vertex shader; same text weight in both spaces.
• draw.alpha_like_linear, ui.tuned: translucent colors tuned for linear light keep their look in an sRGB frame;
  ui.apply_palette(t, p, space); the UI interpolates its gradients in linear light in both spaces.
• render.linear_to_srgb, render.srgb_to_linear.
• tests/blend_space (WARP pixel tests of both spaces); tests/layers and tests/effects run in both spaces.
• Examples: effects --srgb, transforms --srgb, fidget's Settings > Blending (and --blending=srgb|linear).

Changed

• Corner colors are interpolated premultiplied (a transparent corner no longer darkens a gradient).
• The glyph atlas holds raw coverage (font.GLYPH_GAMMA is gone): the 0.8 exponent is now
  Text_Rendering.coverage_exponent, applied by the shader (same look in Linear).
• The constant buffer of rect.hlsl is 48 bytes (target space, text parameters).
• A translucent window's swap chain color space is set explicitly (SetColorSpace1).