Misc bits

A few things have been happening


Fixed a few bugs in CEPL so a user could start making geometry shaders, AND HE DID :) He is using my inline glsl code as well which was nice to see. Cross platform stuff

Fixed bug in CEPL which resulted from changes to the SDL2 wrapper library I use. The guys making it are awesome but have slightly different philosophy on threading. They want to make it transparent as possible, I want it explicit. Their way is better for starting out or games where you are never going to have to worry about that performance overhead, but I can risk that in CEPL.

The problem that arose was that I was calling their initialization function and was getting additional threads created. To solve this I just called the lower level binding functions myself to initialize sdl2. As ever though huge props to those guys, they are making working with sdl2 great.

I also got a pull request fixing a windows10 issue which I’m super stoked about.

With this CEPL is working on OSX and Windows again

PBR one day..

Crept ever closer to pbr rendering. I am going too damn slowly here. I ran into some issues with my vector-space feature. Currently spaces must be uploaded as uniforms and I don’t have a way to create a new space in the shader code. I also don’t have a way to pass a space from one stage to another. This was an issue as for tangent-space normals you want to make tangent space in the vertex shader and pass it to the fragment shader.

To get past this issue more quickly I added support for the get-transform function on the gpu. The get-transform function takes 2 spaces and returns the matrix4 that transform between them.

This just required modifying the compiler pass that handled space transformation so didnt need much extra code.

Filmic ToneMapping

A mate put me onto this awesome page on ‘Filmic Tonemapping Operators’ and I obviously want to support HDR in my projects so I have converted these samples to lisp code. I just noticed that I havent pushed this library online yet, but I will soon.

The mother of all dumb FBO mistakes

I have been smacking my head against an issue for days and it turned out to be a user level mistake (I was that user :p).

The setup was a very basic deffered setup, so the first pass was packing the gbuffer, the second shading using that gbuffer. But whilst the first pass appeared to be working when drawing to the screen it was failing when drawing to an FBO, the textures were full of garbage that could only have been random gpu data and only one patch seemed to be getting written into.

Now as I havent done that enough testing on the multi render target code I assumed that it must be broken. Some hours of digging later it wasnt looking hopeful.

I tested on my (older) laptop..and it seemed better! There was still some corruption but less and more of the model showing…weird.

This was also the first time working with half-float textures as a render target, so I assumed I had some mistakes there. More hours later no joy either.

Next I had been fairly sure viewports were involved in this bug somehow (given that some of the image looked correct) but try as I might I could not find the damn bug. I tripple checked the size of all the color textures.. and the formats and the binding unbinding in the abstrations.

Nothing. Nada. Zip

Out of desperation I eventually made an fbo and let CEPL set all the defaults except size…AND IT WORKED…what the fuck?!

I looked back at my code that initialized the FBO and finally saw it:

    (make-fbo `(0 :dimensions ,dim :element-type :rgb16f)
              `(1 :dimensions ,dim :element-type :rgb16f)
              `(2 :dimensions ,dim :element-type :rgb8)
              `(3 :dimensions ,dim :element-type :rgb8)

That :d in there is telling CEPL to make a depth attachment, and to use some sensible defaults. However it also is going to pick a size, which as a default will be the size of the current viewport *smashes face into table*

According to the GL spec:

If the attachment sizes are not all identical, rendering will be limited to the largest area that can fit in all of the attachments (an intersection of rectangles having a lower left of (0 0) and an upper right of (width height) for each attachment).

Which explains everything I was seeing.

As it is more usual to make attachments the same size I now require a flag to be set if you want attachments with different sizes along with a big ol’ explanation of this issue in the error message you see if you don’t set the flag.


With that madness out of the way I fancy a drink. Seeya all later!

Published: July 10 2016

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