Allow specifying image opacity via graphics state. Support ExtGState when merging content streams (in blocks).

pdf/creator/block.go

@@ -8,6 +8,8 @@ package creator
 import (
 	"errors"
 
+	"fmt"
+
 	"github.com/unidoc/unidoc/pdf/contentstream"
 	"github.com/unidoc/unidoc/pdf/core"
 	"github.com/unidoc/unidoc/pdf/model"
@@ -348,6 +350,7 @@ func mergeContents(contents *contentstream.ContentStreamOperations, resources *m
 	xobjectMap := map[core.PdfObjectName]core.PdfObjectName{}
 	fontMap := map[core.PdfObjectName]core.PdfObjectName{}
 	csMap := map[core.PdfObjectName]core.PdfObjectName{}
+	gstateMap := map[core.PdfObjectName]core.PdfObjectName{}
 
 	for _, op := range *contentsToAdd {
 		switch op.Operand {
@@ -432,6 +435,35 @@ func mergeContents(contents *contentstream.ContentStreamOperations, resources *m
 					op.Params[0] = &useName
 				}
 			}
+		case "gs":
+			// ExtGState.
+			if len(op.Params) == 1 {
+				if name, ok := op.Params[0].(*core.PdfObjectName); ok {
+					if _, processed := gstateMap[*name]; !processed {
+						var useName core.PdfObjectName
+						// Process if not already processed.
+						gs, found := resourcesToAdd.GetExtGState(*name)
+						if found {
+							useName = *name
+							i := 1
+							for {
+								gs2, found := resources.GetExtGState(useName)
+								if !found || gs == gs2 {
+									break
+								}
+								useName = core.PdfObjectName(fmt.Sprintf("GS%d", i))
+								i++
+							}
+						}
+
+						resources.AddExtGState(useName, gs)
+						gstateMap[*name] = useName
+					}
+
+					useName := gstateMap[*name]
+					op.Params[0] = &useName
+				}
+			}
 		}
 
 		*contents = append(*contents, op)

pdf/creator/image.go

@@ -38,6 +38,9 @@ type image struct {
 	xPos float64
 	yPos float64
 
+	// Opacity (alpha value).
+	opacity float64
+
 	// Margins to be applied around the block when drawing on Page.
 	margins margins
 
@@ -71,6 +74,7 @@ func NewImage(data []byte) (*image, error) {
 	image.width = image.origWidth
 	image.height = image.origHeight
 	image.angle = 0
+	image.opacity = 1.0
 
 	image.positioning = positionRelative
 
@@ -131,6 +135,11 @@ func (img *image) Width() float64 {
 	return img.width
 }
 
+// Set opacity
+func (img *image) SetOpacity(opacity float64) {
+	img.opacity = opacity
+}
+
 // Set the image Margins.
 func (img *image) SetMargins(left, right, top, bottom float64) {
 	img.margins.left = left
@@ -263,7 +272,12 @@ func drawImageOnBlock(blk *Block, img *image, ctx DrawContext) (DrawContext, err
 	// Graphics state with normal blend mode.
 	gs0 := core.MakeDict()
 	gs0.Set("BM", core.MakeName("Normal"))
-	err = blk.resources.AddExtGState(gsName, gs0)
+	if img.opacity < 1.0 {
+		gs0.Set("CA", core.MakeFloat(img.opacity))
+		gs0.Set("ca", core.MakeFloat(img.opacity))
+	}
+
+	err = blk.resources.AddExtGState(gsName, core.MakeIndirectObject(gs0))
 	if err != nil {
 		return ctx, err
 	}