有两种主要方法可以旋转页面内容并使其显示在查看器中,就像旋转发生在可见页面的中间一样：任何一个实际上都是通过将旋转与平移连接在一起而绕其中间旋转,或者一个移动裁剪框使页面区域中心跟随旋转.

实际上围绕中心旋转

为此,我们将两个平移之间的旋转包围起来,第一个将坐标系的原点移动到页面中心,第二个将其再次移回.

PDDocument document = PDDocument.load(resource);

PDPage page = document.getDocumentCatalog().getPages().get(0);

PDPageContentStream cs = new PDPageContentStream(document, page, PDPageContentStream.AppendMode.PREPEND, false, false);

PDRectangle cropBox = page.getCropBox();

float tx = (cropBox.getLowerLeftX() + cropBox.getUpperRightX()) / 2;

float ty = (cropBox.getLowerLeftY() + cropBox.getUpperRightY()) / 2;

cs.transform(Matrix.getTranslateInstance(tx, ty));

cs.transform(Matrix.getRotateInstance(Math.toRadians(45), 0, 0));

cs.transform(Matrix.getTranslateInstance(-tx, -ty));

cs.close();

(RotatePageContent test testRotateCenter)

显然,您可以将矩阵相乘并仅向PDF添加单个转换.

拉动裁剪框

为此,我们计算页面中心的移动并相应地移动框.

PDDocument document = PDDocument.load(resource);

PDPage page = document.getDocumentCatalog().getPages().get(0);

PDPageContentStream cs = new PDPageContentStream(document, page, PDPageContentStream.AppendMode.PREPEND, false, false);

Matrix matrix = Matrix.getRotateInstance(Math.toRadians(45), 0, 0);

cs.transform(matrix);

cs.close();

PDRectangle cropBox = page.getCropBox();

float cx = (cropBox.getLowerLeftX() + cropBox.getUpperRightX()) / 2;

float cy = (cropBox.getLowerLeftY() + cropBox.getUpperRightY()) / 2;

Point2D.Float newC = matrix.transformPoint(cx, cy);

float tx = (float)newC.getX() - cx;

float ty = (float)newC.getY() - cy;

page.setCropBox(new PDRectangle(cropBox.getLowerLeftX() + tx, cropBox.getLowerLeftY() + ty, cropBox.getWidth(), cropBox.getHeight()));

PDRectangle mediaBox = page.getMediaBox();

page.setMediaBox(new PDRectangle(mediaBox.getLowerLeftX() + tx, mediaBox.getLowerLeftY() + ty, mediaBox.getWidth(), mediaBox.getHeight()));

(RotatePageContent测试testRotateMoveBox)

缩小内容以适应旋转后的效果

如果想要缩小旋转的内容以使其完全适合,可以将其作为第一个变体的简单扩展：

PDDocument document = PDDocument.load(resource);

PDPage page = document.getDocumentCatalog().getPages().get(0);

PDPageContentStream cs = new PDPageContentStream(document, page, PDPageContentStream.AppendMode.PREPEND, false, false);

Matrix matrix = Matrix.getRotateInstance(Math.toRadians(45), 0, 0);

PDRectangle cropBox = page.getCropBox();

float tx = (cropBox.getLowerLeftX() + cropBox.getUpperRightX()) / 2;

float ty = (cropBox.getLowerLeftY() + cropBox.getUpperRightY()) / 2;

Rectangle rectangle = cropBox.transform(matrix).getBounds();

float scale = Math.min(cropBox.getWidth() / (float)rectangle.getWidth(), cropBox.getHeight() / (float)rectangle.getHeight());

cs.transform(Matrix.getTranslateInstance(tx, ty));

cs.transform(matrix);

cs.transform(Matrix.getScaleInstance(scale, scale));

cs.transform(Matrix.getTranslateInstance(-tx, -ty));

cs.close();

(RotatePageContent测试testRotateCenterScale)

更改裁剪框以使所有以前的页面区域保持可见

如果想要改变裁剪框以使所有东西都适合而不进行缩放,可以将其作为第二种变体的简单扩展：

PDDocument document = PDDocument.load(resource);

PDPage page = document.getDocumentCatalog().getPages().get(0);

PDPageContentStream cs = new PDPageContentStream(document, page, PDPageContentStream.AppendMode.PREPEND, false, false);

Matrix matrix = Matrix.getRotateInstance(Math.toRadians(45), 0, 0);

cs.transform(matrix);

cs.close();

PDRectangle cropBox = page.getCropBox();

Rectangle rectangle = cropBox.transform(matrix).getBounds();

PDRectangle newBox = new PDRectangle((float)rectangle.getX(), (float)rectangle.getY(), (float)rectangle.getWidth(), (float)rectangle.getHeight());

page.setCropBox(newBox);

page.setMediaBox(newBox);

(RotatePageContent测试testRotateExpandBox)

样本结果

下图显示了上述每种方法的输出：

>实际上围绕中心旋转

>在旋转后缩小内容以适应

>拉动裁剪框

>更改裁剪框以使所有以前的页面区域保持可见

图像4与其他图像的尺寸不同,它应该显示更大.