如何將多個轉換套用至物件

若要在物件上執行多個轉換，表示將數個轉換合併成一個轉換。 也就是說，從每個轉換矩陣取得輸出，並將其作為下一個轉換的輸入，藉此取得所有矩陣轉換的累積效果。

假設兩個轉換矩陣，即旋轉矩陣和平移矩陣，彼此相乘。 結果是執行旋轉和轉譯函式的新矩陣。 因為矩陣乘法不具有交換性，旋轉變換乘以平移變換與平移變換乘以旋轉變換不同。

下列程式代碼範例示範如何套用旋轉，後面接著翻譯，然後轉譯接著旋轉。 請注意，轉譯結果不同。

D2D1_RECT_F rectangle = D2D1::RectF(300.0f, 40.0f, 360.0f, 100.0f);

// Draw the rectangle before transforming the render target.

m_pRenderTarget->DrawRectangle(
    rectangle,
    m_pOriginalShapeBrush,
    1.0f,
    m_pStrokeStyleDash
    );

D2D1_MATRIX_3X2_F rotation = D2D1::Matrix3x2F::Rotation(
    45.0f,
    D2D1::Point2F(330.0f, 70.0f)
    );


D2D1_MATRIX_3X2_F translation = D2D1::Matrix3x2F::Translation(20.0f, 10.0f);

// First rotate about the center of the square and then move
// 20 pixels to the right along the x-axis
// and 10 pixels downward along the y-axis.
m_pRenderTarget->SetTransform(rotation* translation);

// Draw the rectangle in the transformed space.
m_pRenderTarget->FillRectangle(rectangle, m_pFillBrush);
m_pRenderTarget->DrawRectangle(rectangle, m_pTransformedShapeBrush, 1.0f);

D2D1_RECT_F rectangle = D2D1::Rect(40.0f, 40.0f, 100.0f, 100.0f);

// Draw a rectangle without transforming it.
m_pRenderTarget->DrawRectangle(
    rectangle,
    m_pOriginalShapeBrush,
    1.0f,
    m_pStrokeStyleDash
    );

D2D1_MATRIX_3X2_F translation = D2D1::Matrix3x2F::Translation(20.0f, 10.0f);

m_pRenderTarget->SetTransform(translation);

D2D1_MATRIX_3X2_F rotation = D2D1::Matrix3x2F::Rotation(
    45.0f,
    D2D1::Point2F(70.0f, 70.0f)
    );

// First move 20 pixels to the right along the x-axis and
// 10 pixels downward along the y-axis,
// and then rotate about the center of the original square.
m_pRenderTarget->SetTransform(translation * rotation);

// Draw the rectangle in the transformed space.
m_pRenderTarget->FillRectangle(rectangle, m_pFillBrush);
m_pRenderTarget->DrawRectangle(rectangle, m_pTransformedShapeBrush);

此程式代碼會產生下圖所示的輸出。

相關主題

Direct2D 參考

Direct2D 轉換概述