Constant GLYPH_FRAG 

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