How D2D implement scroll screen function?

Question

I tried to use Direct2D in our map application. But it is much more slower than GDI because D2D draw the whole screen. When user scroll the window, GDI scroll the video buffer and ONLY draw a small portion of screen. That is why GDI is faster than D2D.

My questions are:

• How D2D scroll screen? (Similar to ScrollWindow())
• How I only draw a small portion of screen in D2D? (Similar to InvalidateRect() and GetClipBox())

I found a solution in How to scroll window contents using Direct2D api? Does anyone have a better solution?

My example is:

D2D1::Matrix3x2F matrix;
CPoint org(GetDeviceScrollPosition());
FLOAT scaleW=(FLOAT)m_totalLog.cx/m_totalDev.cx;
FLOAT scaleH=(FLOAT)m_totalLog.cy/m_totalDev.cy;

if(scaleW > scaleH) scaleW = scaleH;
matrix.SetProduct(D2D1::Matrix3x2F::Scale(scaleW, scaleH, D2D1::Point2F(0.0f, 0.0f)),     D2D1::Matrix3x2F::Translation((FLOAT)-org.x, (FLOAT)-org.y));
//"Scale Device Screen" * "Scroll Device Screen"
pRenderTarget->SetTransform(matrix);

in CScrollView. But the performance is very poor.

Answer 1

I found one solution: Using "CDCRenderTarget". Then we can use the scroll/GetClipBox() functions in CScrollView.

void CMFCGdi_D2D2View::OnDraw(CDC* pDC)
{
    CMFCGdi_D2D2Doc* pDoc = GetDocument();
    ASSERT_VALID(pDoc);
    if (!pDoc) return;

    // TODO: add draw code for native data here
    #define LINE_WIDTH  3

    CRect rcInvalid;
    pDC->GetClipBox(rcInvalid);
    if(rcInvalid.left==0 && rcInvalid.top==0) pDC->FillSolidRect(rcInvalid, RGB(255,0,0));
    else pDC->FillSolidRect(rcInvalid, RGB(0, 255, 0)); //visible redraw area

    CRect rcLogical;
    GetClientRect(rcLogical);
    rcLogical.bottom+=GetScrollPosition().y;
    rcLogical.right+=GetScrollPosition().x;

    m_RenderTarget.BindDC(*pDC, rcLogical);
    m_RenderTarget.BeginDraw();
    m_RenderTarget.SetTransform(D2D1::Matrix3x2F::Identity());
    m_RenderTarget.DrawEllipse(CD2DEllipse(CD2DPointF(150.0f, 150.0f), CD2DSizeF(100., 100.)), m_pBlackBrush, LINE_WIDTH);
    m_RenderTarget.DrawLine(CD2DPointF(150.0f, 150.0f), CD2DPointF(150.0f + 100.0f * 0.15425f, 150.0f - 100.0f * 0.988f),
        m_pBlackBrush, LINE_WIDTH);
    m_RenderTarget.DrawLine(CD2DPointF(150.0f, 150.0f), CD2DPointF(150.0f + 100.0f * 0.525f, 150.0f + 100.0f * 0.8509f),
        m_pBlackBrush, LINE_WIDTH);
    m_RenderTarget.DrawLine(CD2DPointF(150.0f, 150.0f), CD2DPointF(150.0f - 100.0f * 0.988f, 150.0f - 100.0f * 0.15425f),
        m_pBlackBrush, LINE_WIDTH);
    HRESULT hr = m_RenderTarget.EndDraw();

    if (SUCCEEDED(hr))
    {
        // Draw the pie chart with GDI.
        CPen penBlack(PS_SOLID, LINE_WIDTH, RGB(255, 0, 0));
        CPen* pOldPen = pDC->SelectObject(&penBlack);

        pDC->Ellipse(300, 50, 500, 250);

        POINT pntArray1[2];
        pntArray1[0].x = 400;
        pntArray1[0].y = 150;
        pntArray1[1].x = static_cast<LONG>(400 + 100 * 0.15425);
        pntArray1[1].y = static_cast<LONG>(150 - 100 * 0.9885);

        POINT pntArray2[2];
        pntArray2[0].x = 400;
        pntArray2[0].y = 150;
        pntArray2[1].x = static_cast<LONG>(400 + 100 * 0.525);
        pntArray2[1].y = static_cast<LONG>(150 + 100 * 0.8509);

        POINT pntArray3[2];
        pntArray3[0].x = 400;
        pntArray3[0].y = 150;
        pntArray3[1].x = static_cast<LONG>(400 - 100 * 0.988);
        pntArray3[1].y = static_cast<LONG>(150 - 100 * 0.15425);

        pDC->Polyline(pntArray1, 2);
        pDC->Polyline(pntArray2, 2);
        pDC->Polyline(pntArray3, 2);

        pDC->SelectObject(&pOldPen);
    }
}