Scale retro terminal scan lines (#4716)

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## Summary of the Pull Request
- Scale the retro terminal effects (#3468) scan lines with the screen's DPI.
- Remove artifacts from sampling wrap around.

Before & after, with my display scale set to 350%:
![Scaling scan lines](https://user-images.githubusercontent.com/38924837/75214566-df0f4780-5742-11ea-9bdc-3430eb24ccca.png)

Before & after showing artifact removal, with my display scale set to 100%, and image enlarged to 400%:
![Sampling artifacts annotated](https://user-images.githubusercontent.com/38924837/75214618-05cd7e00-5743-11ea-9060-f4eba257ea56.png)

<!-- Please review the items on the PR checklist before submitting-->
## PR Checklist
* [x] Closes #4362
* [x] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [ ] Tests added/passed
* [ ] Requires documentation to be updated
* [ ] I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

<!-- Provide a more detailed description of the PR, other things fixed or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

Adds a constant buffer, which could be used for other settings for the retro terminal pixel shader.

I haven't touched C++ in over a decade before this change, and this is the first time I've played with DirectX, so please assume my code isn't exactly best practice. 🙂

<!-- Describe how you validated the behavior. Add automated tests wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

- Changed display scale with experimental.retroTerminalEffect enabled, enjoyed scan lines on high resolution monitors.
- Enabled experimental.retroTerminalEffect, turned the setting off, changed display scale. Retro tabs still scale scan lines.

src/renderer/dx/DxRenderer.cpp

@@ -286,12 +286,24 @@ HRESULT DxEngine::_SetupTerminalEffects()
 
     RETURN_IF_FAILED(_d3dDevice->CreateBuffer(&bd, &InitData, &_screenQuadVertexBuffer));
 
+    D3D11_BUFFER_DESC pixelShaderSettingsBufferDesc{};
+    pixelShaderSettingsBufferDesc.Usage = D3D11_USAGE_DEFAULT;
+    pixelShaderSettingsBufferDesc.ByteWidth = sizeof(_pixelShaderSettings);
+    pixelShaderSettingsBufferDesc.BindFlags = D3D11_BIND_CONSTANT_BUFFER;
+
+    _ComputePixelShaderSettings();
+
+    D3D11_SUBRESOURCE_DATA pixelShaderSettingsInitData{};
+    pixelShaderSettingsInitData.pSysMem = &_pixelShaderSettings;
+
+    RETURN_IF_FAILED(_d3dDevice->CreateBuffer(&pixelShaderSettingsBufferDesc, &pixelShaderSettingsInitData, &_pixelShaderSettingsBuffer));
+
     // Sampler state is needed to use texture as input to shader.
     D3D11_SAMPLER_DESC samplerDesc{};
     samplerDesc.Filter = D3D11_FILTER_MIN_MAG_MIP_LINEAR;
-    samplerDesc.AddressU = D3D11_TEXTURE_ADDRESS_WRAP;
-    samplerDesc.AddressV = D3D11_TEXTURE_ADDRESS_WRAP;
-    samplerDesc.AddressW = D3D11_TEXTURE_ADDRESS_WRAP;
+    samplerDesc.AddressU = D3D11_TEXTURE_ADDRESS_CLAMP;
+    samplerDesc.AddressV = D3D11_TEXTURE_ADDRESS_CLAMP;
+    samplerDesc.AddressW = D3D11_TEXTURE_ADDRESS_CLAMP;
     samplerDesc.MipLODBias = 0.0f;
     samplerDesc.MaxAnisotropy = 1;
     samplerDesc.ComparisonFunc = D3D11_COMPARISON_ALWAYS;
@@ -308,6 +320,22 @@ HRESULT DxEngine::_SetupTerminalEffects()
     return S_OK;
 }
 
+// Routine Description:
+// - Puts the correct values in _pixelShaderSettings, so the struct can be
+//   passed the GPU.
+// Arguments:
+// - <none>
+// Return Value:
+// - <none>
+void DxEngine::_ComputePixelShaderSettings() noexcept
+{
+    // Retro scan lines alternate every pixel row at 100% scaling.
+    _pixelShaderSettings.ScaledScanLinePeriod = _scale * 1.0f;
+
+    // Gaussian distribution sigma used for blurring.
+    _pixelShaderSettings.ScaledGaussianSigma = _scale * 2.0f;
+}
+
 // Routine Description;
 // - Creates device-specific resources required for drawing
 //   which generally means those that are represented on the GPU and can
@@ -1097,18 +1125,18 @@ void DxEngine::_InvalidOr(RECT rc) noexcept
 // - S_OK on success, E_PENDING to indicate a retry or a relevant DirectX error
 [[nodiscard]] HRESULT DxEngine::Present() noexcept
 {
-    if (_retroTerminalEffects)
+    if (_presentReady)
     {
-        const HRESULT hr2 = _PaintTerminalEffects();
-        if (FAILED(hr2))
+        if (_retroTerminalEffects)
         {
-            _retroTerminalEffects = false;
-            LOG_HR_MSG(hr2, "Failed to paint terminal effects. Disabling.");
+            const HRESULT hr2 = _PaintTerminalEffects();
+            if (FAILED(hr2))
+            {
+                _retroTerminalEffects = false;
+                LOG_HR_MSG(hr2, "Failed to paint terminal effects. Disabling.");
+            }
         }
-    }
 
-    if (_presentReady)
-    {
         try
         {
             HRESULT hr = S_OK;
@@ -1492,6 +1520,7 @@ try
     _d3dDeviceContext->PSSetShader(_pixelShader.Get(), nullptr, 0);
     _d3dDeviceContext->PSSetShaderResources(0, 1, shaderResource.GetAddressOf());
     _d3dDeviceContext->PSSetSamplers(0, 1, _samplerState.GetAddressOf());
+    _d3dDeviceContext->PSSetConstantBuffers(0, 1, _pixelShaderSettingsBuffer.GetAddressOf());
     _d3dDeviceContext->Draw(ARRAYSIZE(_screenQuadVertices), 0);
 
     return S_OK;
@@ -1589,6 +1618,16 @@ CATCH_RETURN()
 
     RETURN_IF_FAILED(InvalidateAll());
 
+    if (_retroTerminalEffects && _d3dDeviceContext && _pixelShaderSettingsBuffer)
+    {
+        _ComputePixelShaderSettings();
+        try
+        {
+            _d3dDeviceContext->UpdateSubresource(_pixelShaderSettingsBuffer.Get(), 0, NULL, &_pixelShaderSettings, 0, 0);
+        }
+        CATCH_RETURN();
+    }
+
     return S_OK;
 }
 

src/renderer/dx/DxRenderer.hpp

@@ -188,13 +188,23 @@ namespace Microsoft::Console::Render
         ::Microsoft::WRL::ComPtr<ID3D11PixelShader> _pixelShader;
         ::Microsoft::WRL::ComPtr<ID3D11InputLayout> _vertexLayout;
         ::Microsoft::WRL::ComPtr<ID3D11Buffer> _screenQuadVertexBuffer;
+        ::Microsoft::WRL::ComPtr<ID3D11Buffer> _pixelShaderSettingsBuffer;
         ::Microsoft::WRL::ComPtr<ID3D11SamplerState> _samplerState;
         ::Microsoft::WRL::ComPtr<ID3D11Texture2D> _framebufferCapture;
 
         D2D1_TEXT_ANTIALIAS_MODE _antialiasingMode;
 
+        // DirectX constant buffers need to be a multiple of 16; align to pad the size.
+        __declspec(align(16)) struct
+        {
+            float ScaledScanLinePeriod;
+            float ScaledGaussianSigma;
+#pragma warning(suppress : 4324) // structure was padded due to __declspec(align())
+        } _pixelShaderSettings;
+
         [[nodiscard]] HRESULT _CreateDeviceResources(const bool createSwapChain) noexcept;
         HRESULT _SetupTerminalEffects();
+        void _ComputePixelShaderSettings() noexcept;
 
         [[nodiscard]] HRESULT _PrepareRenderTarget() noexcept;
 

src/renderer/dx/ScreenPixelShader.h

@@ -7,8 +7,13 @@ const char screenPixelShaderString[] = R"(
 Texture2D shaderTexture;
 SamplerState samplerState;
 
+cbuffer PixelShaderSettings
+{
+    float ScaledScanLinePeriod;
+    float ScaledGaussianSigma;
+};
+
 #define SCANLINE_FACTOR 0.5
-#define SCANLINE_PERIOD 1
 
 static const float M_PI = 3.14159265f;
 
@@ -26,7 +31,6 @@ float4 Blur(Texture2D input, float2 tex_coord, float sigma)
     float texelHeight = 1.0f/height;
 
     float4 color = { 0, 0, 0, 0 };
-    float factor = 1;
 
     int sampleCount = 13;
 
@@ -49,7 +53,7 @@ float4 Blur(Texture2D input, float2 tex_coord, float sigma)
 
 float SquareWave(float y)
 {
-    return 1 - (floor(y / SCANLINE_PERIOD) % 2) * SCANLINE_FACTOR;
+    return 1 - (floor(y / ScaledScanLinePeriod) % 2) * SCANLINE_FACTOR;
 }
 
 float4 Scanline(float4 color, float4 pos)
@@ -74,7 +78,7 @@ float4 main(float4 pos : SV_POSITION, float2 tex : TEXCOORD) : SV_TARGET
 
     // TODO:GH#3930 Make these configurable in some way.
     float4 color = input.Sample(samplerState, tex);
-    color += Blur(input, tex, 2)*0.3;
+    color += Blur(input, tex, ScaledGaussianSigma)*0.3;
     color = Scanline(color, pos);
 
     return color;