From fbda7aab230dfce5804c2d4bd3b27e7d146beefd Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Fri, 7 Aug 2020 22:20:01 -0400
Subject: [PATCH] Does just enough to get the correct (aspect ratio aside)
 output of scan outlines.

So, up next, can I start streaming these things?
---
 .../Clock Signal/ScanTarget/CSScanTarget.mm   | 12 +++++------
 .../Clock Signal/ScanTarget/ScanTarget.metal  | 21 ++++++++++++++++++-
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/OSBindings/Mac/Clock Signal/ScanTarget/CSScanTarget.mm b/OSBindings/Mac/Clock Signal/ScanTarget/CSScanTarget.mm
index a806938c7..76f774a6f 100644
--- a/OSBindings/Mac/Clock Signal/ScanTarget/CSScanTarget.mm	
+++ b/OSBindings/Mac/Clock Signal/ScanTarget/CSScanTarget.mm	
@@ -42,10 +42,10 @@ constexpr size_t NumBufferedScans = 2048;
 
 		// Install the standard quad.
 		constexpr float vertices[] = {
-			-0.9f,	-0.9f,
-			-0.9f,	0.9f,
-			0.9f,	-0.9f,
-			0.9f,	0.9f,
+			0.0f,	0.0f,
+			0.0f,	1.0f,
+			1.0f,	0.0f,
+			1.0f,	1.0f,
 		};
 		_quadBuffer = [view.device newBufferWithBytes:vertices length:sizeof(vertices) options:MTLResourceCPUCacheModeDefaultCache];
 
@@ -53,7 +53,7 @@ constexpr size_t NumBufferedScans = 2048;
 		_uniformsBuffer = [view.device newBufferWithLength:16 options:MTLResourceCPUCacheModeWriteCombined];
 		const Uniforms testUniforms = {
 			.scale = {1024, 1024},
-			.lineWidth = 0.1f
+			.lineWidth = 1.0f / 312.0f
 		};
 		[self setUniforms:testUniforms];
 
@@ -99,7 +99,7 @@ constexpr size_t NumBufferedScans = 2048;
 	scans[1].scan.end_points[0].x = 0;
 	scans[1].scan.end_points[0].y = 768;
 	scans[1].scan.end_points[1].x = 512;
-	scans[1].scan.end_points[1].y = 128;
+	scans[1].scan.end_points[1].y = 512;
 
 	memcpy(_scansBuffer.contents, scans, sizeof(scans));
 }
diff --git a/OSBindings/Mac/Clock Signal/ScanTarget/ScanTarget.metal b/OSBindings/Mac/Clock Signal/ScanTarget/ScanTarget.metal
index e95180d9c..e4610583e 100644
--- a/OSBindings/Mac/Clock Signal/ScanTarget/ScanTarget.metal	
+++ b/OSBindings/Mac/Clock Signal/ScanTarget/ScanTarget.metal	
@@ -53,8 +53,27 @@ vertex ColouredVertex scanVertexMain(	QuadInputVertex vert [[stage_in]],
 										constant Uniforms &uniforms [[buffer(1)]],
 										constant Scan *scans [[buffer(2)]],
 										ushort instance [[instance_id]]) {
+	// Unpack start and end vertices.
+	const float2 start = float2(
+		float(scans[instance].startPosition & 0xffff) / float(uniforms.scale.x),
+		float(scans[instance].startPosition >> 16) / float(uniforms.scale.y)
+	);
+	const float2 end = float2(
+		float(scans[instance].endPosition & 0xffff) / float(uniforms.scale.x),
+		float(scans[instance].endPosition >> 16) / float(uniforms.scale.y)
+	);
+
+	// Calculate the tangent and normal.
+	const float2 tangent = end - start;
+	const float2 normal = float2(-tangent.y, tangent.x) / length(tangent);
+
+	// Hence determine this quad's real shape.
 	ColouredVertex output;
-	output.position = float4(vert.position * uniforms.lineWidth, 0.0, 1.0);
+	output.position = float4(
+		(start + vert.position.x * tangent + vert.position.y * normal * uniforms.lineWidth) * float2(2.0, -2.0) + float2(-1.0, 1.0),
+		0.0,
+		1.0
+	);
 	return output;
 }