how to get the (s,s1) in the arrow?using direct2d?

Question

I draw a line and I know the two points one of them is (x,y) and then I want to draw arraw. and I can not get the axis of the (s,s1) because the arraw may have different directions.

Answer 1

With the help of ChatGPT, this works for me :

// Helper function to subtract two D2D1_POINT_2F points
D2D1_POINT_2F SubtractPoints(D2D1_POINT_2F p1, D2D1_POINT_2F p2)
{
	return D2D1::Point2F(p1.x - p2.x, p1.y - p2.y);
}

// Helper function to add two D2D1_POINT_2F points
D2D1_POINT_2F AddPoints(D2D1_POINT_2F p1, D2D1_POINT_2F p2)
{
	return D2D1::Point2F(p1.x + p2.x, p1.y + p2.y);
}

void DrawLineWithArrow(ID2D1DeviceContext* pDeviceContext, ID2D1Brush* pBrush, D2D1_POINT_2F startPoint,
	D2D1_POINT_2F endPoint,	float arrowSize)
{
	// Draw the line
	pDeviceContext->DrawLine(startPoint, endPoint, pBrush);

	// Calculate the direction vector and normalize it
	D2D1_POINT_2F direction = D2D1::Point2F(endPoint.x - startPoint.x, endPoint.y - startPoint.y);
	float length = sqrtf(direction.x * direction.x + direction.y * direction.y);
	direction.x /= length;
	direction.y /= length;

	// Calculate the points of the arrowhead
	D2D1_POINT_2F arrowBase1 = D2D1::Point2F(
		direction.x * arrowSize + direction.y * arrowSize,
		direction.y * arrowSize - direction.x * arrowSize
	);
	D2D1_POINT_2F arrowBase2 = D2D1::Point2F(
		direction.x * arrowSize - direction.y * arrowSize,
		direction.y * arrowSize + direction.x * arrowSize
	);

	D2D1_POINT_2F left = SubtractPoints(endPoint, arrowBase1);
	D2D1_POINT_2F right = SubtractPoints(endPoint, arrowBase2);

	// Retrieve the factory from the device context
	ID2D1Factory* pFactory = nullptr;
	pDeviceContext->GetFactory(&pFactory);

	// Create a path geometry for the arrowhead
	ID2D1PathGeometry* pArrowGeometry = nullptr;
	HRESULT hr = pFactory->CreatePathGeometry(&pArrowGeometry);
	if (SUCCEEDED(hr))
	{
		ID2D1GeometrySink* pSink = nullptr;
		hr = pArrowGeometry->Open(&pSink);
		if (SUCCEEDED(hr))
		{
			pSink->BeginFigure(endPoint, D2D1_FIGURE_BEGIN_FILLED);
			pSink->AddLine(left);
			pSink->AddLine(right);
			pSink->EndFigure(D2D1_FIGURE_END_CLOSED);
			pSink->Close();
			pSink->Release();
		}
	}

	// Draw the arrowhead
	if (pArrowGeometry)
	{
		pDeviceContext->FillGeometry(pArrowGeometry, pBrush);
		pArrowGeometry->Release();
	}

	if (pFactory)
	{
		pFactory->Release();
	}
}