Ellipse.hlsl

matrix orthoProjMatrix;
float4 elementSize;
float4 strokeWidth;
float4 ellipseParams;

struct VertexShaderInput
{
    float3 position : POSITION0;
    float4 color : COLOR0;
    float2 texCoord : TEXCOORD0;
};

struct PixelShaderInput
{
    float4 position : POSITION0;
    float2 texCoord : TEXCOORD0;
    float4 color : TEXCOORD1;
};

void VertexMain(in VertexShaderInput vsInput, out PixelShaderInput output)
{
    output = (PixelShaderInput)0;

    output.position = mul(float4(vsInput.position, 1), orthoProjMatrix);
    output.texCoord = vsInput.texCoord;
    output.color = vsInput.color;
}

float getEllipseRadius(float x, float y)
{
    float phi = atan2(y, x);
    float a2 = ellipseParams.x * ellipseParams.x;
    float b2 = ellipseParams.y * ellipseParams.y;
    float ab = ellipseParams.x * ellipseParams.y;
    float sin2 = sin(phi) * sin(phi);
    float cos2 = cos(phi) * cos(phi);

    return (ab) / sqrt(a2 * sin2 + b2 * cos2);
}

void PixelMain(in PixelShaderInput input, out float4 color : COLOR0)
{
    float elemX = (-elementSize.x / 2.0f) + elementSize.x * input.texCoord.x;
    float elemY = (-elementSize.y / 2.0f) + elementSize.y * input.texCoord.y;

    float radius = getEllipseRadius(elemX, elemY);
    float radiusCoord = sqrt(elemX * elemX + elemY * elemY);
    if(radiusCoord <= radius)
        color = input.color;
    else
        color = float4(0, 0, 0, 0);
}