add small, colored border shader (#635)

* Create lightgun-border.slang

* Create lightgun-border.slangp

border/lightgun-border.slangp

@@ -0,0 +1,5 @@
+shaders = 1
+
+shader0 = shaders/lightgun-border.slang
+scale_type0 = viewport
+scale0 = 1.0

border/shaders/lightgun-border.slang

@@ -0,0 +1,66 @@
+#version 450
+
+layout(push_constant) uniform Push
+{
+	vec4 SourceSize;
+	vec4 OriginalSize;
+	vec4 OutputSize;
+	uint FrameCount;
+	uint TotalSubFrames;
+	uint CurrentSubFrame;
+	vec4 FinalViewportSize;
+	float bordersize, bordercolor;
+} params;
+
+#pragma parameter bordersize "Border Thickness" 0.02 0.0 1.0 0.01
+#pragma parameter bordercolor "Border Color" 1.0 1.0 6.0 1.0
+int col = int(params.bordercolor);
+
+const vec4 red = vec4(1.,0.,0.,1.);
+const vec4 magenta = vec4(1.,0.,1.,1.);
+const vec4 green = vec4(0.,1.,0.,1.);
+const vec4 blue = vec4(0.,0.,1.,1.);
+const vec4 cyan = vec4(0.,1.,1.,1.);
+const vec4 yellow = vec4(1.,1.,0.,1.);
+
+layout(std140, set = 0, binding = 0) uniform UBO
+{
+	mat4 MVP;
+} global;
+
+#pragma stage vertex
+layout(location = 0) in vec4 Position;
+layout(location = 1) in vec2 TexCoord;
+layout(location = 0) out vec2 vTexCoord;
+layout(location = 1) out vec4 sindenBorder;
+layout(location = 2) out vec4 borderCol;
+
+void main()
+{
+   gl_Position = global.MVP * Position;
+   vTexCoord = TexCoord;
+   float borderthick = params.bordersize * 0.25;
+   // aspect-corrected width
+   sindenBorder.x = borderthick * (params.FinalViewportSize.y * params.FinalViewportSize.z);
+   sindenBorder.y = 1.-sindenBorder.x;
+   sindenBorder.z = borderthick;
+   sindenBorder.w = 1.-borderthick;
+   if(col == 2) borderCol = yellow;
+   else if(col == 3) borderCol = green;
+   else if(col == 4) borderCol = cyan;
+   else if(col == 5) borderCol = blue;
+   else if(col == 6) borderCol = magenta;
+   else borderCol = red;
+}
+
+#pragma stage fragment
+layout(location = 0) in vec2 vTexCoord;
+layout(location = 1) in vec4 sindenBorder;
+layout(location = 2) in vec4 borderCol;
+layout(location = 0) out vec4 FragColor;
+layout(set = 0, binding = 2) uniform sampler2D Source;
+
+void main()
+{
+	FragColor = (vTexCoord.x < sindenBorder.x || vTexCoord.x > sindenBorder.y || vTexCoord.y < sindenBorder.z || vTexCoord.y > sindenBorder.w) ? borderCol : texture(Source, vTexCoord);
+}