使用 PDShadingType4 Apache pdf 框实现 Type 4 阴影

Question

我一直在尝试使用 apache pdf 框在 pdf 中创建一个三角形。使用 PDShadingType4 class。下面是代码实现，但它只创建了空的 pdf。我没有在 apache 提供的示例中找到 PDShadingType4 的任何实现。

生成的三角形应该看起来像 pdf 左下角的三角形 link which is found in apache pdf box issue

我找不到任何使用 PDShadingType4 的着色示例。

下面的实现是否正确？或者他们是使用 PDShadingType4

实现着色（三角形）的其他方法


    import java.io.IOException;
    import org.apache.pdfbox.cos.COSArray;
    import org.apache.pdfbox.cos.COSFloat;
    import org.apache.pdfbox.cos.COSInteger;
    import org.apache.pdfbox.cos.COSName;
    import org.apache.pdfbox.cos.COSStream;
    import org.apache.pdfbox.pdmodel.PDDocument;
    import org.apache.pdfbox.pdmodel.PDPage;
    import org.apache.pdfbox.pdmodel.PDPageContentStream;
    import org.apache.pdfbox.pdmodel.common.function.PDFunctionType2;
    import org.apache.pdfbox.pdmodel.graphics.color.PDDeviceRGB;
    import org.apache.pdfbox.pdmodel.graphics.shading.PDShading;
    import org.apache.pdfbox.pdmodel.graphics.shading.PDShadingType4;

    public class TriangleGraident2 {

        public void create(String file) throws IOException {
            PDDocument document = null;
            try {
                document = new PDDocument();
                PDPage page = new PDPage();
                document.addPage(page);

                PDPageContentStream contentStream = new PDPageContentStream(document, page, PDPageContentStream.AppendMode.APPEND, false);

                contentStream.moveTo(38, 17);

                COSStream fdict = new COSStream();
                fdict.setInt(COSName.FUNCTION_TYPE, 2);

                COSArray cosArray = new COSArray();
                cosArray.add(COSInteger.get(104));
                cosArray.add(COSInteger.get(83));
                cosArray.add(COSInteger.get(170));
                cosArray.add(COSInteger.get(17));
                cosArray.add(COSInteger.get(38));
                cosArray.add(COSInteger.get(17));


                /*Setting color */
                COSArray c0 = new COSArray();
                c0.add(COSFloat.get("1"));
                c0.add(COSFloat.get("0"));
                c0.add(COSFloat.get("0"));
                COSArray c1 = new COSArray();
                c1.add(COSFloat.get("0.5"));
                c1.add(COSFloat.get("1"));
                c1.add(COSFloat.get("0.5"));
                /*Setting color*/


                COSArray decode = new COSArray();
                decode.add(COSFloat.get("0.0"));
                decode.add(COSFloat.get("1.0"));
                decode.add(COSFloat.get("0.0"));
                decode.add(COSFloat.get("1.0"));
                decode.add(COSFloat.get("0.0"));

                fdict.setItem(COSName.C0, c0);
                fdict.setItem(COSName.C1, c1);

                PDFunctionType2 func = new PDFunctionType2(fdict);
                PDShadingType4 shading = new PDShadingType4(fdict);
                shading.setColorSpace(PDDeviceRGB.INSTANCE);
                shading.setShadingType(PDShading.SHADING_TYPE4);

                shading.getCOSObject().setInt(COSName.LENGTH, 32);

                shading.setBitsPerCoordinate(24);
                shading.setBitsPerComponent(16);
                shading.setBitsPerFlag(8);
                shading.getCOSObject().setItem(COSName.COORDS, cosArray);
                shading.setDecodeValues(decode);
                shading.setFunction(func);
                contentStream.shadingFill(shading);
                contentStream.close();
                document.save(file);
                document.close();

            }
            finally {
                if (document != null) {
                    document.close();
                }
            }
        }

        public static void main(String[] args) throws IOException {
            TriangleGraident2 creator = new TriangleGraident2();
            creator.create("C:\Users\abc\Desktop\triangle_image.pdf");
        }
    }

Answer 1

这段代码在左下角创建了一个 Gouraud 阴影三角形：

// See PDF 32000 specification,
// 8.7.4.5.5 Type 4 Shadings (Free-Form Gouraud-Shaded Triangle Meshes)
PDShadingType4 gouraudShading = new PDShadingType4(new COSStream());
gouraudShading.setShadingType(PDShading.SHADING_TYPE4);
// we use multiple of 8, so that no padding is needed
gouraudShading.setBitsPerFlag(8);
gouraudShading.setBitsPerCoordinate(16);
gouraudShading.setBitsPerComponent(8);
COSArray decodeArray = new COSArray();
// coordinates x y map 16 bits 0..FFFF to 0..FFFF to make your life easy
// so no calculation is needed, but you can only use integer coordinates
// for real numbers, you'll need smaller bounds, e.g. 0xFFFF / 0xA = 0x1999
// would allow 1 point decimal result coordinate.
// See in PDF specification: 8.9.5.2 Decode Arrays
decodeArray.add(COSInteger.ZERO);
decodeArray.add(COSInteger.get(0xFFFF));
decodeArray.add(COSInteger.ZERO);
decodeArray.add(COSInteger.get(0xFFFF));
// colors r g b map 8 bits from 0..FF to 0..1
decodeArray.add(COSInteger.ZERO);
decodeArray.add(COSInteger.ONE);
decodeArray.add(COSInteger.ZERO);
decodeArray.add(COSInteger.ONE);
decodeArray.add(COSInteger.ZERO);
decodeArray.add(COSInteger.ONE);
gouraudShading.setDecodeValues(decodeArray);
gouraudShading.setColorSpace(PDDeviceRGB.INSTANCE);

// Function is not required for type 4 shadings and not really useful, 
// because if a function would be used, each edge "color" of a triangle would be one value, 
// which would then transformed into n color components by the function so it is 
// difficult to get 3 "extremes".

OutputStream os = ((COSStream) gouraudShading.getCOSObject()).createOutputStream();
MemoryCacheImageOutputStream mcos = new MemoryCacheImageOutputStream(os);

// Vertex 1, starts with flag1
// (flags always 0 for vertices of start triangle)
mcos.writeByte(0);
// x1 y1 (left corner)
mcos.writeShort(0);
mcos.writeShort(0);
// r1 g1 b1 (red)
mcos.writeByte(0xFF);
mcos.writeByte(0);
mcos.writeByte(0);

// Vertex 2, starts with flag2
mcos.writeByte(0);
// x2 y2 (top corner)
mcos.writeShort(100);
mcos.writeShort(100);
// r2 g2 b2 (green)
mcos.writeByte(0);
mcos.writeByte(0xFF);
mcos.writeByte(0);

// Vertex 3, starts with flag3
mcos.writeByte(0);
// x3 y3 (right corner)
mcos.writeShort(200);
mcos.writeShort(0);
// r3 g3 b3 (blue)
mcos.writeByte(0);
mcos.writeByte(0);
mcos.writeByte(0xFF);

mcos.close();
// outside stream MUST be closed as well, see javadoc of MemoryCacheImageOutputStream
os.close();

到运行的底纹，调用

contentStream.shadingFill(gouraudShading);

这是一个不同的解码数组，类似于您 link 示例 PDF 中的解码数组，尽管我只使用了 16 位而不是 24 位：

COSArray decodeArray = new COSArray();
// coordinates x y map 16 bits 0..FFFF to -16384..16384
// this means that 0x8000 maps to 0
// some other useful values
//  - 0x862C maps to top of A4 page
//  - 0x84C4 maps to right of A4 page
//  - 0x8262 maps to horizontal middle of A4 page
decodeArray.add(COSInteger.get(-16384));
decodeArray.add(COSInteger.get(16384));
decodeArray.add(COSInteger.get(-16384));
decodeArray.add(COSInteger.get(16384));
// colors r g b map 8 bits from 0..FF to 0..1
decodeArray.add(COSInteger.ZERO);
decodeArray.add(COSInteger.ONE);
decodeArray.add(COSInteger.ZERO);
decodeArray.add(COSInteger.ONE);
decodeArray.add(COSInteger.ZERO);
decodeArray.add(COSInteger.ONE);
gouraudShading.setDecodeValues(decodeArray);

三角形的坐标将是 0x8000 0x8000、0x8100 0x8100、0x8200 0x8000。

使用 PDShadingType4 Apache pdf 框实现 Type 4 阴影

Implement Type 4 shadings using PDShadingType4 Apache pdf box

java

apache

pdfbox