I want to draw large width lines using triangular primitives. As the number of vertices rises, the frame rate goes down sharply.The following code is the way to draw primitive and the shader.
Vertex structure
struct Point
{
var position:float2
var color:float4
init() {
position = float2(0, 0)
color = float4(0,0,0,0)
}
init(position:float2,color:float4) {
self.position = position
self.color = color
}
}
struct Line
{
var begin:Point
var end:Point
}Draw method
commandEncoder?.drawPrimitives(type: .triangleStrip, vertexStart: 0, vertexCount: (size - 1) * 4 , instanceCount: size - 1)Shader code
#include <metal_stdlib>
using namespace metal;
struct InputVertex {
float2 position;
float4 color;
};
struct Vertex {
float4 position [[position]];
float4 color;
};
struct Point
{
float2 position;
float4 color;
};
struct Line
{
Point begin;
Point end;
};
struct XCoord
{
float beginX ;
float endX ;
float leftX ;
float rightX ;
float x;
};
struct Uniforms {
float4x4 modelMatrix;
};
vertex Vertex vertex_func(constant Line *lines [[buffer(0)]],
constant Uniforms &uniforms [[buffer(1)]],
uint vertexId [[vertex_id]],
uint instanceId [[instance_id]]) {
float4x4 matrix = uniforms.modelMatrix;
float thickness = 0.004;
Line line = lines[instanceId];
uint index = vertexId % 4;
float4 startPosition = matrix * float4(line.begin.position.x,line.begin.position.y ,0 ,1);
float4 endPosition = matrix * float4(line.end.position.x,line.end.position.y ,0 ,1);
float4 position;
float4 color;
float4 v = endPosition - startPosition;
float2 p0 = float2(startPosition.x,startPosition.y);
float2 v0 = float2(v.x,v.y);
float2 v1 = thickness * normalize(v0) * float2x2(float2(0,-1),float2(1,0));
if (index == 0)
{
float2 pa = p0 + v1;
position = float4(pa.x,pa.y,0,1);
color = line.begin.color;
}
else if (index == 1)
{
float2 pb = p0 - v1;
position = float4(pb.x,pb.y,0,1);
color = line.begin.color;
}
else if (index == 2)
{
float2 pc = p0 - v1 + v0;
position = float4(pc.x,pc.y,0,1);
color = line.end.color;
}
else if (index == 3)
{
float2 pd = p0 + v1 + v0;
position = float4(pd.x,pd.y,0,1);
color = line.end.color;
}
else
{
float2 pd = p0 + v1 + v0;
position = float4(pd.x,pd.y,0,1);
color = line.end.color;
}
Vertex out;
out.position = position;
out.color = color;
return out;
}
fragment float4 fragment_func(Vertex vert [[stage_in]]) {
return vert.color;
}
