Design Pattern for Image and Text Composition in Go

Go Conference Tokyo 2019 Spring

Transcript

1. Design pattern 
 for Image and text composition in Go Go Conference 2019 Spring
 @__timakin__
2. SEIJI TAKAHASHI Software Engineer at Gunosy Inc.
3. Agenda > Image and font packages > Design pattern for composition > Conclusions
4. There are so much stuff to do when you composite image resources and generate a new one.
5. Scope for this talk is … > Workflow of image composition > How to implement them along with the separation of concerns.
6. Scope for this talk is … Timakin Timakin
7. Not scope for this talk ... > The detail of the image package > Image processing except composition
8. Image and font packages
9. Quick Question Have you ever used the image package?
10. package “image” > Package image implements a basic 2-D image library. • Encodes/decodes formats such as GIF, JPEG or PNG. > Provides below interfaces • An inspection of data in the pixels • Adds a color to the specified range • Composition, mask and quantization.
11. e.g. Draw a red rectangle
12. golang.org/x/image/font > Package which defines an interface for font faces, for drawing text on an image. > font.Face is an interface that represents a content of the file of font face. > font.Drawer reads it and draws text on a destination image. > Opentype is not suitable for font.Drawer.
13. github.com/golang/freetype/truetype > Package which provides a parser for the TTF and TTC file formats. > When you would like to flexibly set a font face to font.Drawer, this package will really help you. > A lot of .ttf/.ttc files don’t pass the parse process. • PostScript font type • Hiragino Sans…
14. Design pattern of image composition
15. Workflow of composition > To generate this name card, 
 you have to • Initialize a frame • Draw images • Attach labels • Encode a jpeg output
16. Interfaces Processor Initialize a frame Draw images Attach labels Encode a jpeg output Framer Drawer Labeler Encoder
17. Roles of each structs Framer Drawer Labeler Encoder
18. Processor > Loads fixture images and pass
 them to Drawer. > Includes Framer, Drawer,
 Encoder as fields.
19. Loading fixtures > github.com/rakyll/statik is better if your fixtures are not so large to save the loading time.
20. Insertion of dependent structs > Optional values • Main Thumbnail • Sub image • Background image • Labels • Color • Font family/size • Output path
21. Framer > Initializes *image.RGBA 
 as a canvas. > Width & height, and 
 a background color are required.
22. Fill the RGBA frame with colors
23. Drawer > Receiving the frame, drawer draws fixture and specified images.
24. Call drawing and labeling functions inside > Labeler is called inside of Drawer. • The positions of the texts are calculated by relative value to the images.
25. Call drawing and labeling functions inside Sometimes you have to guard an unexpected-sized images, so drawing function often contains a resizer.
26. Labeler > Labeler attaches a text label with the options. (coordinate, font- family, text alignment etc)
27. Loading assets and font.Drawer > After loading font assets, call truetype font parser with options of size and color.
28. A minor adjustment of text position 
 with fixed.PointXX_xx
29. Encoder > Encoder just calls encode function the image package. > The role of this interface is to abstract the difference between each formats.
31. Conclusion > Image and text compression becomes really messy if you don’t care about the separation of concerns. • Separation by the role becomes easy if you simplify the process. > Composition process deeply depends on a coordinate calculation. Designing optional values is the essential for a simple code.
32. Thank you for listening