I need sample code to insert an Image into a page.

[nonchan7720]

Hello.

I am trying to create a new PDF document and create a one page PDF with one image.
I have created a page in the wasm version of pdfium and inserted an image, but it just shows a blank page and no image.

The procedure is as follows

• Generate a new PDF document with FPDF_CreateNewDocument
• Creation of Image object with FPDFPageObj_NewImageObj
• Specify jpeg byte array and length in FPDFImageObj_LoadJpegFile
• Get size from FPDFImageObj_GetImagePixelSize
• Set Matrix from the size obtained by FPDFImageObj_SetMatrix
• Generate page with FPDFPage_New
• Specify Image object in FPDFPage_InsertObject
• Generate content with FPDFPage_GenerateContent

I am trying to do the above, but it is not working properly, so I would like to have a sample code made.

[jerbob92]

Hi! Can you give me your Go code so I can see what's wrong with it?

[nonchan7720]

@jerbob92
Thanks for the reply.
This is the kind of code we are working on.

type matrix struct {
	a float32
	b float32
	c float32
	d float32
	e float32
	f float32
}

func newMatrix(a, b, c, d, e, f float32) *matrix {
	m := matrix{
		a: a,
		b: b,
		c: c,
		d: d,
		e: e,
		f: f,
	}
	if m.a == 0 {
		m.a = 1
	}
	if m.d == 0 {
		m.d = 1
	}

	return &m
}

func newDefaultMatrix() *matrix {
	return newMatrix(0, 0, 0, 0, 0, 0)
}

func (m *matrix) multiply(other *matrix) *matrix {
	return newMatrix(
		m.a*other.a+m.b*other.c,
		m.a*other.b+m.b*other.d,
		m.c*other.a+m.d*other.c,
		m.c*other.b+m.d*other.d,
		m.e*other.a+m.f*other.c+other.e,
		m.e*other.b+m.f*other.d+other.f,
	)
}

func (m *matrix) scale(x, y float32) *matrix {
	return m.multiply(newMatrix(x, 0, 0, y, 0, 0))
}

func newImageToPage(ctx context.Context, doc references.FPDF_DOCUMENT, imageBuffer []byte) error {
	instance := GetInstance(ctx)
	img, err := instance.FPDFPageObj_NewImageObj(&requests.FPDFPageObj_NewImageObj{
		Document: doc,
	})
	if err != nil {
		return err
	}
	imgObject := img.PageObject
	defer closePageObject(ctx, imgObject)
	_, err = instance.FPDFImageObj_LoadJpegFile(&requests.FPDFImageObj_LoadJpegFile{
		ImageObject:    imgObject,
		FileReader:     bytes.NewReader(imageBuffer),
		FileReaderSize: int64(len(imageBuffer)),
	})
	if err != nil {
		return err
	}
	size, err := instance.FPDFImageObj_GetImagePixelSize(&requests.FPDFImageObj_GetImagePixelSize{
		ImageObject: imgObject,
	})
	if err != nil {
		return err
	}
	m := newDefaultMatrix().scale(float32(size.Width), float32(size.Height))
	_, err = instance.FPDFImageObj_SetMatrix(&requests.FPDFImageObj_SetMatrix{
		ImageObject: imgObject,
		Transform: structs.FPDF_FS_MATRIX{
			A: m.a,
			B: m.b,
			C: m.c,
			D: m.d,
			E: m.e,
			F: m.f,
		},
	})
	if err != nil {
		return err
	}
	page, err := instance.FPDFPage_New(&requests.FPDFPage_New{
		Document: doc,
		Width:    float64(size.Width),
		Height:   float64(size.Height),
	})
	if err != nil {
		return err
	}
	defer ClosePage(ctx, page.Page)
	_, err = instance.FPDFPage_InsertObject(&requests.FPDFPage_InsertObject{
		Page: requests.Page{
			ByReference: &page.Page,
		},
		PageObject: imgObject,
	})
	if err != nil {
		return err
	}
	_, err = instance.FPDFPage_GenerateContent(&requests.FPDFPage_GenerateContent{
		Page: requests.Page{
			ByReference: &page.Page,
		},
	})
	if err != nil {
		return err
	}
	if err != nil {
		return err
	}
	return nil
}

[nonchan7720]

@jerbob92
I'd be happy to check 🙏.

[jerbob92]

I have looked into it and this seems to be an issue with the WebAssembly version, when I try it in the CGO version it does work, I will investigate a bit more and add some tests for it.

[nonchan7720]

Thank you for investigating this.
Is this not supported on the Wasm side and there is nothing I can do with this library?

[jerbob92]

Everything is supported in both implementations, WASM and CGO, that it is not working is a bug.

[nonchan7720]

I wish I could help, but my lack of skills makes it difficult to modify this library yet.

[jerbob92]

I haven't figured it out yet, but:

• It can load the image fine in WebAssembly, I have validated this by checking the pixel size with FPDFImageObj_GetImagePixelSize and actually rendering the bitmap in Go with FPDFImageObj_GetBitmap/FPDFBitmap_GetBuffer, and the image looks like what it should be
• The image object is added to the PDF content
• The image object content (XObject) is not added to the PDF content

[jerbob92]

This should be fixed in v1.6.1!

[nonchan7720]

Thank you!
If I have any problems I will let you know👍

[jerbob92]

What I do want to add:
You seem to be mixing pixel sizes (from FPDFImageObj_GetImagePixelSize) with point sizes (in the matrix and FPDFPage_New). This should work, but it will make a very big PDF (in terms of inches), and if you want to add anything else to the page it might give you some issues.

[nonchan7720]

I see, thanks.
I was referring to this.
https://github.com/pypdfium2-team/pypdfium2

[jerbob92]

Ah I see, yes that example has the same issue.

Basically it just makes the page the same size in points (inches) as the image is in pixels. Normally you would have something like 72 dots (pixels) per inch. I think they just make them the same to make the example very easy to use/read, but it might look a little odd if you mix it with normally sized pages and/or add other things to the same page.