#version 330

/* A fragment shader: Grayscale Filter with Alpha Exclusion */

precision highp float;		// High quality

// Draw directly to the screen rather than to an off-screen framebuffer
layout(location = 0) out vec4 colorOut;

uniform sampler2D sampler;	// Texture sampler
uniform float alphaCutOff;	// Alpha values below this get discarded

in vec3 texCoord;

void main(void)
{
	vec4 texColor = texture(sampler, texCoord.xy);
	if(texColor.a < alphaCutOff)
		discard;

	// Grayscale intensity = Average of a pixel's RGB components
	float intensity = (texColor.r + texColor.g + texColor.b) / 3.0;
	
	// Output the fragment
	colorOut = vec4(intensity, intensity, intensity, texColor.a);

	const int numViewports = gl_MaxViewports;	// Error line
}