// ---------------------- Vertex Shader for line primitives -------------------------

// --- Input Constants ---
// vc0, vc1, vc2, vc3 	- 4x4 model matrix
// vc4, vc5, vc6, vc7 	- 4x4 view matrix
// vc8.x				- Scalar for LineThickness

// --- Input Attributes ---
// va0 		- 3d vector of vertex position
// va1 		- 3d vector of line direction
// va2.x	- Dash size

// --- Usage ---
// Each line is represented by 4 vertices - two at the start point, and two at the end point.
// This shader will move these vertices apart, so as to form a rectangle,
// so index buffers should be populated as if these 4 vertices form a quad.

// ----------------------------------------------------------------------------------

// Transform vertex by model matrix
m44 vt5 va0 vc0

// Copy model matrix to temporary registers, where we are allowed to manipulate it
mov vt0 vc0
mov vt1 vc1
mov vt2 vc2
mov vt3 vc3

// Remove translation - we don't want to translate a vector that holds direction (not position)
sub vt0.w vt0.w vt0.w
sub vt1.w vt1.w vt1.w
sub vt2.w vt2.w vt2.w

// Transform line direction by the model matrix - save in vt4
m44 vt4 va1 vt0

// Line direction is now in 2d screen space, take its right orthagonal and put it in vt2.xy
mov vt2 vt4					// Copy to prevent shader validation error
mov vt2.x vt4.y				// Transpose X & Y
mov vt2.y vt4.x				// Transpose X & Y
neg vt2.y vt2.y 			// y = -y

// Normalize the direction down to 1 pixel, then multiply it by LineThickness
mul vt0.xy vt2.xy vt2.xy	// Square offset
add vt0.z vt0.x vt0.y		// Sum of squares
sqt vt0.z vt0.z				// Square root - save in vt0.z
//div vt2.xy vt2.xy vt0.z		// Normalize offset
//mul vt2.xy vt2.xy vc8.x		// Multiply by LineThickness

// Shift the screen space vertex by the 2d direction
add vt5.xy vt5.xy vt2.xy	// Add offset to transformed vertex position

// Set up dash size
div vt0.z vt0.z	va2.x	// Change dash size to length relative
mov v0 vt0.z					// Copy the vertex distance on line to the fragment shader
//mov v0.x va2.x					// Copy the vertex distance on line to the fragment shader

// Transform by view matrix
m44 vt5 vt5 vc4				// Transform by view
mov op vt5					// Return vertex position