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#pragma once
#include <mbgl/shader/attributes.hpp>
#include <mbgl/util/geometry.hpp>
#include <cmath>
namespace mbgl {
struct LineAttributes : gl::Attributes<
attributes::a_pos,
attributes::a_data<4>> {
/*
* @param p vertex position
* @param e extrude normal
* @param t texture normal
* @param dir direction of the line cap (-1/0/1)
*/
static Vertex vertex(Point<int16_t> p, Point<double> e, Point<bool> t, int8_t dir, int32_t linesofar = 0) {
return Vertex {
{
static_cast<int16_t>((p.x * 2) | t.x),
static_cast<int16_t>((p.y * 2) | t.y)
},
{
// add 128 to store an byte in an unsigned byte
static_cast<uint8_t>(::round(extrudeScale * e.x) + 128),
static_cast<uint8_t>(::round(extrudeScale * e.y) + 128),
// Encode the -1/0/1 direction value into the first two bits of .z of a_data.
// Combine it with the lower 6 bits of `linesofar` (shifted by 2 bites to make
// room for the direction value). The upper 8 bits of `linesofar` are placed in
// the `w` component. `linesofar` is scaled down by `LINE_DISTANCE_SCALE` so that
// we can store longer distances while sacrificing precision.
// Encode the -1/0/1 direction value into .zw coordinates of a_data, which is normally covered
// by linesofar, so we need to merge them.
// The z component's first bit, as well as the sign bit is reserved for the direction,
// so we need to shift the linesofar.
static_cast<uint8_t>(((dir == 0 ? 0 : (dir < 0 ? -1 : 1 )) + 1) | ((linesofar & 0x3F) << 2)),
static_cast<uint8_t>(linesofar >> 6)
}
};
}
/*
* Scale the extrusion vector so that the normal length is this value.
* Contains the "texture" normals (-1..1). This is distinct from the extrude
* normals for line joins, because the x-value remains 0 for the texture
* normal array, while the extrude normal actually moves the vertex to create
* the acute/bevelled line join.
*/
static const int8_t extrudeScale = 63;
};
using LineVertex = LineAttributes::Vertex;
static_assert(sizeof(LineVertex) == 8, "expected LineVertex size");
} // namespace mbgl
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