varying.def.sc file is too mysterious

[DagAgren]

There's no documentation for the varying.def.sc file format, and it seems to have lots of peculiarities about it. I've run into lots of trouble getting my shaders working because of problems with varying.def.sc. For instance, it seems highly sensitive to whitespace placement. It is also not quite clear what the various parts of it actually mean.

[bkaradzic]

White space is probably bug. What's exact problem?

Format is:

 [lowp/mediump/highp] [flat/smooth/noperspective] <type> <name> : <semantics> [= default value];

[DagAgren]

I got problems when I did not have spaces around : and =. Parsing seemed to fail and no varying statement was added to the source.

[DagAgren]

Also, right now, both my $input and $output values are being declared as "varying" for some reason I can't figure out.

$input vertex_attrib
$output position

#include <bgfx_shader.sh>

uniform vec3 size;

void main()
{
    position=vertex_attrib*size;
    gl_Position=mul(u_modelViewProj,vec4(position,1.0));
}

varying.def.sc:

vec3 position : POSITION = vec3(0.0,0.0,0.0);

vec3 vertex_attrib : POSITION;

And with options --type v --platform osx --profile 120.

[DagAgren]

The result is:

varying vec3 vertex_attrib;
varying vec3 position;
uniform mat4 u_modelViewProj;
uniform vec3 size;
void main ()
{
  position = (vertex_attrib * size);
  vec4 tmpvar_1;
  tmpvar_1.w = 1.0;
  tmpvar_1.xyz = position;
  gl_Position = (u_modelViewProj * tmpvar_1);
}

[bkaradzic]

vertex_attrib is invalid name for attribute ($input). It must be one of following:
https://github.com/bkaradzic/bgfx/blob/master/include/bgfx.h#L72

For $output you can name varying as you like.

[bkaradzic]

I fixed varying parsing.

[DagAgren]

Ok, good!

But some documentation would be quite nice, so you can find out that some names are special.

(Is there any reason they have to be? Can't shaderc change the names around if special ones are needed on some platform?)

[bkaradzic]

It's documented in all examples since they are using a_* notation + header file that provides documentation about vertex declaration explicitly states how those are bound to shader.