//
//  ScanTarget.metal
//  Clock Signal
//
//  Created by Thomas Harte on 04/08/2020.
//  Copyright © 2020 Thomas Harte. All rights reserved.
//

#include <metal_stdlib>
using namespace metal;

// These two structs are the same, but defined separately as an artefact
// of my learning process, and the fact that they soon won't be.

struct Uniforms {
	// This is used to scale scan positions, i.e. it provides the range
	// for mapping from scan-style integer positions into eye space.
	int2 scale						[[attribute(0)]];

	// This provides the intended width of a scan, in eye-coordinate terms.
	float lineWidth					[[attribute(1)]];
};

// This is intended to match `Scan` as defined by the BufferingScanTarget.
// Fields have been combined as necessary to make them all at least four
// bytes in size, since that is the required attribute alignment in Swift.
struct Scan {
	uint32_t startPosition			[[attribute(0)]];
	uint32_t startOffsetAndAngle	[[attribute(1)]];
	uint32_t startCycles			[[attribute(2)]];

	uint32_t endPosition			[[attribute(3)]];
	uint32_t endOffsetAndAngle		[[attribute(4)]];
	uint32_t endCycles				[[attribute(5)]];

	uint32_t compositeAmplitude		[[attribute(6)]];
	uint32_t dataYAndLine			[[attribute(7)]];
};

// This is a custom thing defining one corner of a quad.
struct QuadInputVertex {
	float2 position	[[attribute(0)]];
};

struct ColouredVertex {
	float4 position [[position]];
};


// MARK: - Scan shaders; these do final output to the display.

vertex ColouredVertex scanVertexMain(	QuadInputVertex vert [[stage_in]],
										constant Uniforms &uniforms [[buffer(1)]],
										constant Scan *scans [[buffer(2)]],
										ushort instance [[instance_id]]) {
	ColouredVertex output;
	output.position = float4(vert.position * uniforms.lineWidth, 0.0, 1.0);
	return output;
}

fragment float4 scanFragmentMain(ColouredVertex vert [[stage_in]]) {
	return float4(1.0);
}