Babylon.js/canvas2D/src/shaders/lines2d.vertex.fx

// based on if Instanced Array are supported or not, declare the field either as attribute or uniform
#ifdef Instanced
#define att attribute
#else
#define att uniform
#endif

attribute vec2 position;
att vec2 zBias;
att vec4 transformX;
att vec4 transformY;
att vec3 renderingInfo;
att float opacity;

#ifdef FillSolid
att vec4 fillSolidColor;
#endif

#ifdef BorderSolid
att vec4 borderSolidColor;
#endif

#ifdef FillGradient
att vec2 boundingMin;
att vec2 boundingMax;
att vec4 fillGradientColor1;
att vec4 fillGradientColor2;
att vec4 fillGradientTY;
#endif

#ifdef BorderGradient
att vec4 borderGradientColor1;
att vec4 borderGradientColor2;
att vec4 borderGradientTY;
#endif

#define TWOPI 6.28318530

// Output
varying vec2 vUV;
varying vec4 vColor;

void main(void) {

#ifdef FillSolid
	vColor = fillSolidColor;
#endif

#ifdef BorderSolid
	vColor = borderSolidColor;
#endif

#ifdef FillGradient
	float v = dot(vec4((position.xy - boundingMin) / (boundingMax - boundingMin), 1, 1), fillGradientTY);
	vColor = mix(fillGradientColor2, fillGradientColor1, v);	// As Y is inverted, Color2 first, then Color1
#endif

#ifdef BorderGradient
	float v = dot(vec4((position.xy - boundingMin) / (boundingMax - boundingMin), 1, 1), borderGradientTY);
	vColor = mix(borderGradientColor2, borderGradientColor1, v);	// As Y is inverted, Color2 first, then Color1
#endif

	vColor.a *= opacity;
	vec4 pos;
	pos.xy = position.xy;
	pos.z = 1.0;
	pos.w = 1.0;
	
	float x = dot(pos, transformX);
	float y = dot(pos, transformY);
	if (renderingInfo.z == 1.0) {
		float rw = renderingInfo.x;
		float rh = renderingInfo.y;
		float irw = 2.0 / rw;
		float irh = 2.0 / rh;

		x = (floor((x / irw) + 0.5) * irw) + irw / 2.0;
		y = (floor((y / irh) + 0.5) * irh) + irh / 2.0;
	}

	gl_Position = vec4(x, y, zBias.x, 1);
}