Fixup: Removed unsupported floating-point suffix prior to GLSL ES 3.00

[daschuer]

This fixes the issue reported here:
#11982

warning [Main] QOpenGLShader::compile(Fragment): ERROR: 0:7: '0.75f' : Floating-point suffix unsupported prior to GLSL ES 3.00
ERROR: 0:7: '0.75f' : syntax error

[Swiftb0y]

LGTM.

[JoergAtGithub]

Now Angle works when I add precision highp float; (with the black spinnies reported in #11930 - this means this is a 2.4 bug and not a Qt6 regression). But than the normal OpenGL operation is broken. Mixxx asserts before the main window is shown:

warning [Main] QOpenGLShader::compile(Fragment): ERROR: 0:5: '' :  syntax error, unexpected IDENTIFIER
ERROR: 1 compilation errors.  No code generated.


warning [Main] *** Problematic Fragment shader source code ***
#ifdef GL_KHR_blend_equation_advanced
#extension GL_ARB_fragment_coord_conventions : enable
#extension GL_KHR_blend_equation_advanced : enable
#endif
#define lowp
#define mediump
#define highp
#line 1

uniform highp vec4 color;
varying highp float vgradient;
precision highp float;
void main()
{
    float minAlpha = 0.5 * color.w;
    float maxAlpha = 0.83 * color.w;
    gl_FragColor = vec4(color.xyz, mix(minAlpha, maxAlpha, max(0.,vgradient)));
}

***
DEBUG ASSERT: "addShaderFromSourceCode( GLShader::Fragment, fragmentShaderCode)" in function void __cdecl mixxx::Shader::load(const class QString &,const class QString &) at C:\Users\Joerg.WORLDWARTWEB\source\repos\JoergAtGithub\mixxx\src\shaders\shader.cpp:24

[JoergAtGithub]

I found out, that we need to specify
precision highp float;
when using OpenGL ES, but not when using normal OpenGL.

[daschuer]

Yes, that's clear. But In my tests the Qt boilerplate Code defined highp away. Why does this fail in your case?

[daschuer]

Ah I see it is the added:
precision highp float;
This does not work along with
#define highp
It will become
precision float;
and fails.

[Swiftb0y]

yeah, so I guess we can't specify the precision via the default precision precision-qualifier​ type​; but instead need to specify it manually for every variable so it gets #defined away properly?