Precision identifiers in GLSL Fragment shader code generate errors

[Ferobles92]

Hello all,

I am developing an application using the QWindow. In doing so, I started learning OpenGL ES 2.0. I have been learning about shaders and precision. I have the following code for a fragment shader:

@
#ifdef GL_FRAGMENT_PRECISION_HIGH
precision highp float;
#else
precision mediump float;
#endif

varying vec4 color;
void main()
{
gl_FragColor = color;
}
@

I get the following error when I compile this shader code:

QOpenGLShader::compile(Fragment): ERROR: 0:7: 'precision' : syntax error syntax error

Can anyone explain why? According to a book on this type of OpenGL, that is valid code (as a matter of fact, I am borrowing from that book).

Thanks in advance.

[sletta]

Be aware of that QOpenGLShader will insert

@#define highp
#define mediump
#define lowp@

at the top of your glsl code when you are compiling for desktop. And on desktop, 'precision' is not a valid token until one of the later versions (exactly which one I can't remember right now).

So based on that, I'd say that you are compiling for desktop and it fails on line 4 (7 - 3 inserted lines) of your code because 'precision' is not a valid keyword.

QOpenGLShaderProgram tries to help in this regard by defining the precision specifiers to empty on desktop, so if you change your code to:

@lowp varying vec4 color;
void main() {
gl_FragColor = color;
}@

it will compile for both desktop and es.