What if I started fpGUI Toolkit again today? Meet Blaise Canvas UI

[graemeg]

Sneak peek: Blaise Canvas UI, a new cross-platform GUI toolkit written in Blaise

Twenty years ago I started fpGUI with one goal: a GUI toolkit with as few third-party dependencies as possible (no GTK, no Qt) and the same look on every platform. It worked, but some of its design choices show their age. So I asked myself:

If I started from scratch with the Blaise compiler, how would I design a cross-platform GUI toolkit? Would it look like fpGUI, or would I take a different approach?

Blaise Canvas UI is the answer: a new project, not a port of fpGUI. It keeps fpGUI's best ideas and rethinks the rest.

Mini IDE, the code editor example, in the dark theme:

Media player, a video view above a four-track editing timeline:

Highlights

• No third-party dependencies. Custom-drawn widgets on a thin backend per OS. No GTK, no Qt, no FreeType: only the operating system's own interfaces.
• Identical pixels on every platform. A deterministic renderer whose golden-image tests are byte-identical on macOS arm64 and Linux x86-64.
• Built-in fonts and text. Its own font parsing and glyph rendering, embedded Noto fonts, and Unicode bidi and line breaking that pass all ~103,000 Unicode conformance test cases.
• Floating-point coordinates. Fractional scaling (125%, 150%) works properly, with edges snapped to pixels so lines stay crisp.
• Ready for GPU rendering. Widgets record display lists; the software renderer is fast, and GPU renderers (Metal first) plug in without touching widget code.
• Accessibility from day one. Every widget describes itself in a semantic tree, bridged to AT-SPI2 on Linux and NSAccessibility on macOS.
• No nested event loops. Menus, combo boxes and tooltips are drawn inside the window, and dialogs complete through a callback, so the popup problems we fought in fpGUI are gone by design.

More detail on the design

Kept from fpGUI

• Custom-drawn widgets and a universal look: one theme, the same everywhere, with light and dark variants.
• The split between a core layer (windows, events, canvas, fonts) and a widget layer.
• Layouts as objects. Box, grid and stack layouts exist today, built on a two-pass measure/arrange protocol; MiG layout is planned as a later port.

Done differently

• Fonts and text. TrueType and CFF/OpenType parsing, kerning and the basic OpenType substitution and positioning features, Unicode 15.1 tables, grapheme and line breaking, right-to-left text, paragraph layout, input-method composition, undo/redo, and a glyph cache with quarter-pixel positioning. Shaping sits behind an interface, so complex scripts can plug in CoreText, DirectWrite or HarfBuzz as optional extras.
• Display protocols spoken directly. The X11 and Wayland backends implement the wire protocols in Blaise, with no Xlib and no libwayland. The Cocoa backend binds the Objective-C runtime at run time.
• Testing without a display. A headless backend and test driver click, type and inspect widgets through the accessibility tree, then compare screenshots with golden images.
• Modern ownership. ARC throughout: parents own children, back references are [Weak], and typed signals replace single event slots.

Where it stands

• Backends: Cocoa (macOS), Wayland and X11 (Linux), plus headless. The Win32 backend is written and type-checks, and is waiting on Blaise's Windows code generator.
• Widgets: labels, buttons, check and radio buttons, edit and memo, spin edits, sliders, combo boxes, menus and menu bar, toolbars, tabs, splitters, list, tree and table views, file, colour and font dialogs, a syntax-highlighting code editor, and a video view with an editing timeline.
• Performance: in software, a full 1280×800 editor frame renders in about 15 ms and a 4K frame in about 33 ms.
• Size: about 37,000 lines of Blaise, renderer and font engine included, with over 200 automated tests. For comparison, fpGUI is over 200,000 lines, and about half of that is AggPas, written in old-style Pascal objects.

Next: the GPU renderer (Metal first), Windows once Blaise can target it, testing with real screen readers (VoiceOver, Orca), MiG layout, and client-side window decorations.

How it was built

This is AI-assisted coding with human guidance, from design to implementation. I set the goals and made the design decisions, Claude Code wrote most of the code under my review, and every decision is recorded in the design documents.

It also turned out to be the ultimate test application for Blaise. Over 37,000 lines of real GUI code shook out a handful of compiler bugs, on both x86-64 and arm64, and each was promptly fixed upstream.

What about fpGUI?

fpGUI isn't going anywhere. I'll keep maintaining it for the long term; Blaise Canvas UI is a fresh start alongside it, not a replacement.

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This is an early look, not a release yet. I'd love to hear your thoughts: what you'd want from a toolkit like this, which widgets matter most to you, and what you'd build with it.

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Built with ❤ for the Pascal community by Graeme.

[sstillwell]

It would be great if it supported native controls on each platform, but I understand where this is coming from. Accessibility out of the box is chef's kiss. Excited to see the progress, and looking forward to a proper Pascal environment and ecosystem that isn't dragging along 20+ years of baggage.

[graemeg]

a proper Pascal environment and ecosystem that isn't dragging along 20+ years of baggage.

Exactly right! With a new compiler and updated language (out with the old, in with the new), it deserved a new "UI face". 😄 Plus, it is a great test to see how far Blaise has come.

[Schmitty2005]

Canvas widget feature! Lines, rectangles , circles, etc. I will use it as a gui for drawing waveforms. Antialias as well.

I am looking forward to the initial release!

[graemeg]

It shouldn't be too much longer. Just doing some final touches and documentation / tutorial, then I'm make the repo public with v0.1.0 release.

[dioaffriza]

Wow! What a news! That's nice. What I want mostly just CJK and BiDi font rendering that I still have a problem with fpGUI, so I made the entire thing again here https://github.com/kiranaproject/ft. This is very exciting for the Blaise Compiler.

[graemeg]

How did I miss that project?? 🙈 Very impressive! CJK and BiDi is added to Blaise Canvas UI - it was a often requested feature for fpGUI, but hard to retrofit fpGUI, so I never got around to it sadly.

[dioaffriza]

CJK and BiDi added in the work already? Nice! I can't wait to try Blaise Canvas UI when it go public! 😉

About my project, In early stage I just playing with LLM and FpGui's AggPas, somewhat suddenly I have an idea to create the entire desktop environment with UI toolkit included 😂

[graemeg]

Yeah, some 20+ years ago, I was curious how a Edit box in a UI works and renders. I played around to learn more. One thing led to another, and unexpectedly fpGUI was born. 🤣

[sstillwell]

Some of the greatest discoveries began with someone saying "hmmm, that's unusual..." 🙂