Constant GLYPH_FRAG 

pub const GLYPH_FRAG: &str = "// glyph.frag \u{2014} glyph fragment shader\n// Phase 1 stub. Full shader in Phase 1 implementation.\n\n#version 330 core\n\nin vec2 f_uv;\nin vec4 f_color;\nin float f_emission;\nin vec3 f_glow_color;\n\nuniform sampler2D u_atlas;\n\nlayout(location = 0) out vec4 o_color;\nlayout(location = 1) out vec4 o_emission;  // for bloom pass\n\nvoid main() {\n    float alpha = texture(u_atlas, f_uv).r;  // atlas is R8 (greyscale glyph mask)\n    if (alpha < 0.05) discard;\n\n    o_color   = vec4(f_color.rgb * f_color.a, alpha * f_color.a);\n    o_emission = vec4(f_glow_color * f_emission * alpha, 1.0);\n}\n";