CoopAllTheThings/tools/mock_game/render_dx11.cpp

// DX11 backend for the mock game. Renders the animated pattern entirely with region
// clears (ID3D11DeviceContext1::ClearView) so it needs no shaders: an animated full-screen
// background, a moving vertical bar, and the top-left frame-counter block.
#include "render_backend.hpp"

#include <d3d11_1.h>
#include <dxgi1_6.h>
#include <wrl/client.h>

using Microsoft::WRL::ComPtr;

namespace coop::mock
{
namespace
{
class Dx11Backend : public RenderBackend
{
public:
	bool init(HWND hwnd, std::uint32_t width, std::uint32_t height) override
	{
		width_ = width;
		height_ = height;

		const D3D_FEATURE_LEVEL levels[] = {D3D_FEATURE_LEVEL_11_1, D3D_FEATURE_LEVEL_11_0};
		ComPtr<ID3D11DeviceContext> ctx0;
		if (FAILED(D3D11CreateDevice(nullptr, D3D_DRIVER_TYPE_HARDWARE, nullptr, 0, levels,
		                             static_cast<UINT>(std::size(levels)), D3D11_SDK_VERSION,
		                             device_.GetAddressOf(), nullptr, ctx0.GetAddressOf())))
		{
			return false;
		}
		if (FAILED(ctx0.As(&ctx_))) // ClearView needs ID3D11DeviceContext1
		{
			return false;
		}

		ComPtr<IDXGIDevice> dxgi_device;
		ComPtr<IDXGIAdapter> adapter;
		ComPtr<IDXGIFactory2> factory;
		if (FAILED(device_.As(&dxgi_device)) || FAILED(dxgi_device->GetAdapter(adapter.GetAddressOf())) ||
		    FAILED(adapter->GetParent(IID_PPV_ARGS(factory.GetAddressOf()))))
		{
			return false;
		}

		// The mock does trivial work, so it must render UNCAPPED (it's a perf fixture, not a real
		// game) -- a flip-model swapchain only tears free of vsync with ALLOW_TEARING, so require it.
		ComPtr<IDXGIFactory5> factory5;
		BOOL tearing = FALSE;
		if (SUCCEEDED(factory.As(&factory5)))
		{
			factory5->CheckFeatureSupport(DXGI_FEATURE_PRESENT_ALLOW_TEARING, &tearing, sizeof(tearing));
		}
		tearing_ = tearing != 0;

		DXGI_SWAP_CHAIN_DESC1 desc = {};
		desc.Width = width;
		desc.Height = height;
		desc.Format = DXGI_FORMAT_R8G8B8A8_UNORM; // UNORM (not sRGB) so the frame code is exact
		desc.SampleDesc.Count = 1;
		desc.BufferUsage = DXGI_USAGE_RENDER_TARGET_OUTPUT;
		desc.BufferCount = 2;
		desc.SwapEffect = DXGI_SWAP_EFFECT_FLIP_DISCARD;
		desc.Flags = tearing_ ? DXGI_SWAP_CHAIN_FLAG_ALLOW_TEARING : 0u;
		if (FAILED(factory->CreateSwapChainForHwnd(device_.Get(), hwnd, &desc, nullptr, nullptr,
		                                           swap_.GetAddressOf())))
		{
			return false;
		}
		factory->MakeWindowAssociation(hwnd, DXGI_MWA_NO_ALT_ENTER);

		// D3D11 flip-model: GetBuffer(0) stays the live back buffer, so one RTV is reused.
		ComPtr<ID3D11Texture2D> back;
		if (FAILED(swap_->GetBuffer(0, IID_PPV_ARGS(back.GetAddressOf()))) ||
		    FAILED(device_->CreateRenderTargetView(back.Get(), nullptr, rtv_.GetAddressOf())))
		{
			return false;
		}
		return true;
	}

	void render_and_present(std::uint32_t frame) override
	{
		// Animated background: each channel sweeps at a different rate -> constant motion.
		const float bg[4] = {static_cast<float>((frame * 2) % 256) / 255.0f,
		                     static_cast<float>((frame * 3) % 256) / 255.0f,
		                     static_cast<float>((frame * 5) % 256) / 255.0f, 1.0f};
		ctx_->ClearRenderTargetView(rtv_.Get(), bg);

		// Moving vertical bar (obvious motion; a dropped frame makes it jump).
		const float white[4] = {1.0f, 1.0f, 1.0f, 1.0f};
		const LONG span = width_ > 24 ? static_cast<LONG>(width_ - 24) : 1;
		const LONG bx = static_cast<LONG>((frame * 4) % static_cast<std::uint32_t>(span));
		const D3D11_RECT bar = {bx, 0, bx + 24, static_cast<LONG>(height_)};
		ctx_->ClearView(rtv_.Get(), white, &bar, 1);

		// Frame-counter block (top-left): RGB encodes the exact frame number for the test.
		std::uint8_t r = 0, g = 0, b = 0;
		frame_to_rgb(frame, r, g, b);
		const float code[4] = {r / 255.0f, g / 255.0f, b / 255.0f, 1.0f};
		const D3D11_RECT block = {0, 0, static_cast<LONG>(kFrameBlock), static_cast<LONG>(kFrameBlock)};
		ctx_->ClearView(rtv_.Get(), code, &block, 1);

		swap_->Present(0, tearing_ ? DXGI_PRESENT_ALLOW_TEARING : 0u); // uncapped: the mock must be fast
	}

	[[nodiscard]] const char* name() const override
	{
		return "dx11";
	}

private:
	std::uint32_t width_ = 0;
	std::uint32_t height_ = 0;
	bool tearing_ = false;
	ComPtr<ID3D11Device> device_;
	ComPtr<ID3D11DeviceContext1> ctx_;
	ComPtr<IDXGISwapChain1> swap_;
	ComPtr<ID3D11RenderTargetView> rtv_;
};
} // namespace

std::unique_ptr<RenderBackend> create_dx11_backend()
{
	return std::make_unique<Dx11Backend>();
}

} // namespace coop::mock