gui_toolkit 0.26.0

Merge of three branches: the GPU 2D canvas engine, faster image uploads, the window border color. 0.20.0 and 0.21.0 (reserved below for the canvas engine and the uploads) were never released: their content is here.

Added

• A 2D canvas engine on the GPU (render/canvas.odin, canvas_types.odin, canvas.wgsl, module Canvas of tools/shaders, docs/canvas.md), Direct3D 11: render.canvas_texture_create(r, w, h, target, mips) makes a canvas (a render target of premultiplied sRGB-encoded RGBA8, kept) or a source of pixels (canvas_upload); the owner records its drawing in a render.Canvas_List (instances with a geometry, a paint and an operator; commands for clip masks, layers, snapshots, putImageData) and canvas_submit(r, target, &list) replays it in runs of one draw call per operator / source / clip / scissor. Rectangles, rounded rectangles and ellipses have analytic coverage (exact box filter when axis-aligned), polygons 16 N-rook samples on boundary pixels only with the fill rule per sample (the pieces of a stroke never count twice); solid, linear / radial / conic gradients and images (four filters, wrap modes) as paints; the 11 Porter-Duff operators as blend states and the 15 blend modes from a copy of the backdrop; clip masks, layers with color-matrix and gaussian-blur passes (large blurs on reduced images). canvas_read (waits), canvas_read_begin / canvas_read_ready / canvas_read_finish / canvas_read_cancel (polled), canvas_read_mask, canvas_clear, canvas_set_opaque, canvas_supported (false on WebGPU), canvas_stats, canvas_pool_bytes. tests/canvas (12 pixel tests), in tools\test_backends.ps1.
• platform.set_border_color(w, rgb): the color of the 1-pixel border Windows 11 draws around the window (DWMWA_BORDER_COLOR), or nil for the system's. With an integrated title bar the system's border is half transparent along the top edge: a line of whatever lies behind the window showed above the app's tab strip.
• tests/textures (both backends): an unwritten texture is transparent, an opaque upload with a wider stride shows exactly, a translucent one is premultiplied in both spaces, a partial update zeroes the rest, mips follow an opaque upload; render/premultiply_test.odin checks the word-at-a-time premultiplication against (c * a + 127) / 255 for every value. Both in tools\test_backends.ps1.

Changed

• Faster image textures: create_texture_rgba no longer zeroes a new texture with one UpdateSubresource per row (551 driver calls, 1 to 4 ms, for a 735 x 551 photo). The texture is marked unfilled; an update that covers it whole clears the mark, and one still unfilled when the frame is submitted (or hit by a partial update first) is zeroed with a few band-sized calls from one zero buffer (Renderer.zeros). Observable behavior is the same: a new texture is transparent. Data textures (create_texture_data) and video targets keep their own paths.
• Faster uploads: update_texture_rgba checks whether the block is opaque (a vectorized AND of the words) and uploads opaque pixels, which is every JPEG and most PNG / WebP / AVIF, straight from the caller's buffer with its own pitch: no conversion pass and no scratch copy. Translucent blocks in the sRGB blend space are premultiplied a word at a time without branches or tables; the linear space keeps its table version. Both backends.

Fixed

• Windows 11, integrated title bar: a line of what lay behind the window showed above the tab strip, because the system's border is half transparent there. An app now paints it opaque with platform.set_border_color (nothing changes until it does).