Added circle rendering to Renderer2D

Sandbox/content/Shaders/circlebatch.hlsl

@@ -0,0 +1,59 @@
+Texture2D Texture : register(t0);
+SamplerState Sampler : register(s0);
+
+cbuffer Constants : register(b0)
+{
+    float4x4 ViewProjection;
+};
+
+struct VS_Input
+{
+    float2 Position     : POSITION;
+    float2 Texcoord     : TEXCOORD0;
+    float4x4 Transform  : TRANSFORM;
+    float4 Color        : COLOR;
+    float4 UVTransform  : TEXCOORD1;
+    float InnerRadius   : TEXCOORD2;
+};
+
+struct PS_Input
+{
+    float4 Position     : SV_Position;
+    float2 RawPos       : TEXCOORD0;
+    float2 Texcoord     : TEXCOORD1;
+    float4 Color        : COLOR;
+    float InnerRadius   : TEXCOORD2;
+};
+
+PS_Input VS(VS_Input input)
+{
+    PS_Input output;
+
+    output.Position = mul(ViewProjection, mul(input.Transform, float4(input.Position, 0.0f, 1.0f)));
+    output.Texcoord = input.UVTransform.xy + input.UVTransform.zw * input.Texcoord;
+    output.RawPos = input.Position;
+    output.Color = input.Color;
+    output.InnerRadius = input.InnerRadius;
+
+    return output;
+}
+
+float4 PS(PS_Input input) : SV_Target0
+{
+    float2 uv = input.RawPos * 2;
+
+    float distance = 1.0f - length(uv);
+
+    // Smoothing edges based on derivative (not sure if RawPos is the best value for this)
+    float f = fwidth(input.RawPos.x) + fwidth(input.RawPos.y);
+
+    float amount = smoothstep(0.0f, f, distance);
+    amount *= smoothstep(input.InnerRadius + f, input.InnerRadius, distance);
+
+    float4 color = Texture.Sample(Sampler, input.Texcoord) * input.Color;
+    color.a *= amount;
+
+    return color;
+}
+
+#effect[VS=VS, PS=PS]