Shader-based smooth transitions between presets about projectm HOT 5 CLOSED

I actually never looked at the 2.x releases, but this version mostly supported Milkdrop 1.4 presets, which didn't make heavy use of fragment shaders.

Milkdrop has a very complex blending mechanism, deeply built into the rendering pipeline. Basically, if it blends two presets, each rendering step is executed twice and each effect (waveforms, shapes, motion vectors etc.) have their own, individual blending logic. On top of that, Milkdrop also applies some additional effects like a plasma effect to further add some variation into the blending.

In projectM, we opted to not copy/reimplement this process, as it only really works when blending two Milkdrop presets together which use the exact same rendering code. As we're planning to add support for other preset formats (first variants of Milkdrop, e.g. PowerAmp presets) and later on, with version 5, possibly an all-new preset format, we need a more generic blending method which isn't built deeply into the preset rendering code itself.

So what I'm proposing here is using an additional rendering step after both presets finished rendering. In this step, we draw a simple full-screen quad (AKA rectangle), which has a fragment shader that does the actual blending. That means for every pixel in the output, the shader can decide how the pixels from both inputs (textures from the old and new presets) are used and mapped/combined in the final image. The shader knows about the blending percentage, some beat values etc., so it's highly flexible.

In the end, the transitions will not exactly look like those in Milkdrop, but provide us and later the users with more flexibility, e.g. if they can add their own transition shaders and we can easily add other preset formats to the library without having to change this again.

There's one caveat for newly displayed presets: We need to start with the last output frame of the old preset and "seed" the main texture of the new preset to prevent slow-drawing presets from always starting with a black background, but this is easy to implement. We'll also do this with hard cuts to make the transition a bit nicer to look at.

from projectm.

Working branch is here, for those interested in following the progress:
https://github.com/kblaschke/projectm/tree/feature/shader-based-smooth-transitions

Preliminary documentation, will be moved to the Wiki once the feature is finished & polished:
https://gist.github.com/kblaschke/a53952cbaf4e469a0733222f09d6dc1b

from projectm.

Looks good so far! I had a chance to try the shader-based-smooth-transitions at 9a73a88 with a couple different settings for transition timing. Nicely done.

I think the Version 2.x behavior I attempted to describe in a previous message might be the result of the code model you've specifically said was excluded from the current implementation (and I appreciate the reasons why). No matter, though-- the current implementation looks really good in its own way. Will keep an eye on the branch for further work. Thanks!

from projectm.

This sounds really cool, and it relates to a lingering question I've had.

I had been using version 2.x of libprojectm on an older machine, and it seemed like the smooth transitions would progressively blend and eventually replace the old preset with the with one. This created some impressive visuals, especially when setting a long transition time. (I can upload a video clip if this description isn't enough.)

Version 4 of libprojectm is such a huge improvement on single preset rendering, but I've noticed the smooth transitions are not the same, and yes they appear broken when using long transition times.

Would the version 2 behavior, or something like it, be within the scope of what you propose here? I don't know enough C/C++ to contribute to the code, but I'd be glad to help test.

from projectm.

This is excellent news 👍

from projectm.