Constant UI_VERT_SRC 

pub const UI_VERT_SRC: &str = r#"
#version 330 core

layout(location = 0) in vec2  v_pos;
layout(location = 1) in vec2  v_uv;

layout(location = 2)  in vec3  i_position;
layout(location = 3)  in vec2  i_scale;
layout(location = 4)  in float i_rotation;
layout(location = 5)  in vec4  i_color;
layout(location = 6)  in float i_emission;
layout(location = 7)  in vec3  i_glow_color;
layout(location = 8)  in float i_glow_radius;
layout(location = 9)  in vec2  i_uv_offset;
layout(location = 10) in vec2  i_uv_size;

uniform mat4 u_view_proj;

out vec2  f_uv;
out vec4  f_color;
out float f_emission;

void main() {
    float c = cos(i_rotation);
    float s = sin(i_rotation);
    vec2 rotated = vec2(
        v_pos.x * c - v_pos.y * s,
        v_pos.x * s + v_pos.y * c
    ) * i_scale;

    gl_Position = u_view_proj * vec4(i_position + vec3(rotated, 0.0), 1.0);

    f_uv       = i_uv_offset + v_uv * i_uv_size;
    f_color    = i_color;
    f_emission = i_emission;
}
"#;

Vertex shader for UI layer — same as glyph.vert but without Y-flip (the ortho projection handles orientation correctly).