blip.kummerlaender.eu

» Compustream performance improvements and interactive wall drawing

I found some time to further develop my GLSL compute shader based interactive LBM fluid simulation previously described in Fun with compute shaders and fluid dynamics. Not only is it now possible to interactively draw bounce back walls into the running simulation but performance was greatly improved by one tiny line:

glfwSwapInterval(0);

If this function is not called during GLFW window initialization the whole rendering loop is capped to 60 FPS – including compute shader dispatching. This embarrassing oversight on my part caused the simulation to run way slower than possible.

» Describe custom gitolite and cgit setup

Replaces short-term Gitea instance on code.kummerlaender.eu.

The main reason for implementing this more complex setup is that Gitea both lacks in features in areas that I care about and provides distracting features in other areas that I do not use.

e.g. Gitea provides multi-user, discussion and organization support but doesn’t provide Atom feeds which are required for Overview.

This is why exposing gitolite-managed repositories via cgit is a better fit for my usecases.

Note that gitolite is further configured outside of Nix through its own admin repository.

As a side benefit pkgs.kummerlaender.eu now provides further archive formats of its Nix expressions which simplifies Nix channel usage.

» Nixify build process

Building the website in the presence of the Nix package manager is now as simple as:

• cloning this repo
• entering the nix-shell environment declared by shell.nix
• calling generate
• optionally call preview to spawn a webserver in target/99_result

All dependencies such as the internal InputXSLT, StaticXSLT and BuildXSLT modules as well as external ones such as KaTeX and pandoc are built declaratively by Nix.

» Implement particle trails using overlaying textures

» Implement deferred word, conditional resolution

Due to the non-trivial way tokens were previously processed the compiler could not safely perform tail-call elimination. Thus the slang evaluation depth was restricted by the maximum call stack size.

This issue is mitigated by introducing deferred word resolution - i.e. pushing expanded tokens onto a buffer stack and processing them in an explicit loop.

This change ties into the implementation of the language’s conditional primitive. The previous implementation did implicitly not support direct nesting of conditional expressions such as:

truthA if
    mainBranch
    truthB if
        secondaryMainBranch
    then else
then
    alternativeBranch
else

This issue is now made explicit by disallowing direct nesting of conditionals as depicted above. Appropriate exceptions are generated when required and the conditional primitive is reimplemented in a more robust fashion under the assumption that this rule holds. Note that nesting is still fully supported iff. the nested conditional is contained in a deferredly evaluated word. As a positive side effect this will make it slightly harder to generate unreadable code by forcing developers to write simpler words.

The main change of the conditional primitive lies in deferring branch token processing until the conditional expression is concluded by else. This is achieved by capturing non-dropped tokens in an internal buffer akin to how the word definition operator § is implemented. The branch buffer is discharged after else is evaluated. Discharging is triggered via the newly introduced result method of the primitive evaluation module. This avenue for injecting tokens into the processing stream may be used by further primitives in the future.

» Use pandoc as markdown processor

The trigger but not the actual reason for this replacement of kramdown with pandoc was a strange generation issue with kramdown’s latest release.

All recent articles failed to generate anything more than an empty page. A quick check of the resulting HTML for those articles offered nothing out of the ordinary. After taking a close look at the articles in question I narrowed the set of failing articles down to those containing footnotes - tangentially I only started using footnotes a couple of articles ago i.e. this explained this part of the issue.

Some debugging of InputXSLT offered the following problem: Xerces-C generated an error message and stopped processing XML inputs containing nbsp non-blocking space characters in the implementation of the external-command function. This change in kramdown’s output can be traced back to enhancement issue 399. Obviously this is not a problem in kramdown but an issue in the way this static site generator is wrapping HTML inputs.

This problem should be solvable by adding appropriate namespace and doctype declarations to the markdown-generated HTML output. Instead I opted to perform the change to pandoc I had already planned for quite some time.

The choice fell on pandoc as it offers some additional markdown features as well as allowing for conversion to a rich set of document formats. i.e. features like printing articles as PDF using LaTeX are trivial to implement if pandoc is the markdown processor of choice. Furthermore page compilation is noticeably faster using pandoc.

One might note that this switch only solved the original issue by coincidence: Should pandoc start to generate non-blocking space characters the same problem will occur. But I have hopes that such a change would be configurable via pandoc’s plethora of configuration options. As this static site generator assumes everything to be XHTML I see no reason why I should not continue to treat HTML inputs as XML.