如何将多个转换应用于对象

对对象执行多个转换意味着将多个转换合并为一个转换。 也就是说，获取每个转换矩阵的输出，并将其用作下一个矩阵的输入，从而获取所有矩阵转换的累积效果。

假设旋转和平移这两个转换矩阵相乘。 结果是执行旋转和平移功能的新矩阵。 由于矩阵乘法不是可交换的，因此旋转转换乘以平移转换与平移转换乘以旋转转换不同。

下面的代码示例演示如何应用旋转后跟转换，然后应用转换，然后应用旋转。 请注意，呈现结果不同。

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);

代码生成如下图所示的输出。

相关主题

Direct2D 参考

Direct2D 转换概述