I'm looking for help with a little code/shader for an arcade project

// Cocktail Table Portrait
// by hunterk
// license: public domain
 
uniform float width < ui_name = "Cocktail Width"; ui_type = "slider"; ui_min = 0.0; ui_max = 2.0; ui_step = 0.01; > = 1.0;
uniform float height < ui_name = "Cocktail Height"; ui_type = "slider"; ui_min = 0.0; ui_max = 2.0; ui_step = 0.01; > = 0.49;
uniform float x_loc < ui_name = "Cocktail X Mod"; ui_type = "slider"; ui_min = -2.0; ui_max = 2.0; ui_step = 0.01; > = 0.0;
uniform float y_loc < ui_name = "Cocktail Y Mod"; ui_type = "slider"; ui_min = -2.0; ui_max = 2.0; ui_step = 0.01; > = 0.51;
// important for hw-rendered cores
uniform bool flip_y < ui_name = "Flip Vertical Axis"; > = false;
 
uniform texture2D BackBufferTex : COLOR;
uniform sampler2D BackBuffer { Texture = BackBufferTex; };

#define InputSize float2(BUFFER_WIDTH, BUFFER_HEIGHT)
#define OutputSize InputSize
#define TextureSize InputSize

// compatibility #defines
#define Source BackBuffer
#define vTexCoord TEX0.xy
#define SourceSize vec4(TextureSize, 1.0 / TextureSize) //either TextureSize or InputSize
#define OutSize vec4(OutputSize, 1.0 / OutputSize)

void vertex(in uint id : SV_VERTEXID, out float4 gl_Position : SV_POSITION, out float2 TEX0 : TEXCOORD0, out float2 t1 : TEXCOORD1)
{
	float2 TexCoord;
	TexCoord.x = (id == 2) ? 2.0 : 0.0;
	TexCoord.y = (id == 1) ? 2.0 : 0.0;
	gl_Position = float4(TexCoord * float2(2.0, -2.0) + float2(-1.0, 1.0), 0.0, 1.0);

	TEX0.xy = TexCoord.xy;
	TEX0.xy = TEX0.xy - 0.5 * InputSize / TextureSize;
	TEX0.xy = TEX0.xy * float2(1. / width, 1. / height);
	TEX0.xy = TEX0.xy + 0.5 * InputSize / TextureSize;
	t1.xy = 1.* InputSize / TextureSize - TEX0.xy;
	TEX0.xy -= float2(x_loc, y_loc) * InputSize / TextureSize;
	t1.xy -= float2(x_loc, y_loc) * InputSize / TextureSize;
	if(flip_y > 0.5)
	{
		// have to compensate for the slightly reduced height and y_loc values
		TEX0.y += 1.025* InputSize.y / TextureSize.y;
		t1.y += 1.025* InputSize.y / TextureSize.y;
	}
}
  
void fragment(in float4 vpos : SV_POSITION, in float2 TEX0 : TEXCOORD0, in float2 t1 : TEXCOORD1, out float4 FragColor : SV_TARGET)
{
	float4 screen1 = tex2D(Source, vTexCoord);
	screen1 *= float(vTexCoord.x > 0.0001) * float(vTexCoord.y > 0.0001) * float(vTexCoord.x < 0.9999) * float(vTexCoord.y < 0.9999);
	float4 screen2 = tex2D(Source, t1);
	screen2 *= float(t1.x > 0.0001) * float(t1.y > 0.0001) * float(t1.x < 0.9999) * float(t1.y < 0.9999);
	FragColor = screen1 + screen2;
}

technique Cocktail
{
    pass
    {
        VertexShader = vertex;
        PixelShader = fragment;
    }
}

#include "shared/cGraphics.fxh"

/*
[Shader Options]
*/

uniform float _Angle <
ui_label = "Rotation Angle";
ui_type = "drag";
> = 0.0;

uniform float2 _Translate <
ui_label = "Translation";
ui_type = "drag";
> = 0.0;

uniform float2 _Scale <
ui_label = "Scaling";
ui_type = "drag";
> = 1.0;

/*
[Vertex Shaders]
*/

VS2PS_Quad VS_Matrix(APP2VS Input)
{
// Calculate the shader's HPos and Tex0
// We modify the Tex0's output afterward
VS2PS_Quad Output = VS_Quad(Input);

float RotationAngle = radians(_Angle);

float2x2 RotationMatrix = float2x2
(
cos(RotationAngle), -sin(RotationAngle), // Row 1
sin(RotationAngle), cos(RotationAngle) // Row 2
);

float3x3 TranslationMatrix = float3x3
(
1.0, 0.0, 0.0, // Row 1
0.0, 1.0, 0.0, // Row 2
_Translate.x, _Translate.y, 1.0 // Row 3
);

float2x2 ScalingMatrix = float2x2
(
_Scale.x, 0.0, // Row 1
0.0, _Scale.y // Row 2
);

// Scale TexCoord from [0,1] to [-1,1]
Output.Tex0 = Output.Tex0 * 2.0 - 1.0;

// Do transformations here
Output.Tex0 = mul(Output.Tex0, RotationMatrix);
Output.Tex0 = mul(float3(Output.Tex0, 1.0), TranslationMatrix).xy;
Output.Tex0 = mul(Output.Tex0, ScalingMatrix);

// Scale TexCoord from [-1,1] to [0,1]
Output.Tex0 = Output.Tex0 * 0.5 + 0.5;

return Output;
}

/*
[Pixel Shaders]
*/

float4 PS_Matrix(VS2PS_Quad Input) : SV_TARGET0
{
return tex2D(CShade_SampleColorTex, Input.Tex0);
}

technique CShade_Transform
{
pass
{
SRGBWriteEnable = WRITE_SRGB;

VertexShader = VS_Matrix;
PixelShader = PS_Matrix;
}
}