get_arg_vec2
Description:
Gets the value of the uniform idx in the args block.
Note:
GTK's new Vulkan-focused rendering does not support this feature. Use [GtkGLArea](../gtk4/class.GLArea.html) for OpenGL rendering.
The uniform must be of vec2 type.
Parameters:
| this |
a `GskGLShader` |
| args |
uniform arguments |
| idx |
index of the uniform |
| out_value |
location to store the uniform value in |