Add custom font

Custom font could be used together with system font.

This commit also adds pi.LoadFontData which could be used to load font from PNG file into another font instance.

Author: elgopher

examples/print/main.go

@@ -12,8 +12,10 @@ var resources embed.FS
 
 func main() {
 	pi.Resources = resources
+	pi.CustomFont.Width = 6 // set the width of all characters below 128 (ascii)
 	pi.Draw = func() {
-		pi.Print("HELLO,\nWORLD!", 50, 58, 9) // print two lines of yellow text using system font
+		pi.Print("HELLO,\nMY NAME IS", 45, 58, 9)   // print two lines of yellow text using system font
+		pi.CustomFont.Print("PI\u0082", 45, 70, 12) // print blue text with special character using custom font
 	}
 	pi.MustRun()
 }

pi.go

@@ -117,7 +117,7 @@ func Boot() error {
 		return err
 	}
 
-	if err := loadFontData(systemFontPNG, systemFont.Data[:]); err != nil {
+	if err := LoadFontData(systemFontPNG, systemFont.Data[:]); err != nil {
 		return err
 	}
 
@@ -175,6 +175,10 @@ func loadResources(resources fs.ReadFileFS) error {
 		return err
 	}
 
+	if err := loadCustomFont(resources); err != nil {
+		return err
+	}
+
 	return nil
 }
 

pi_test.go

@@ -110,6 +110,18 @@ func TestBoot(t *testing.T) {
 		assert.Equal(t, img.Palette, pi.Palette)
 	})
 
+	t.Run("should load custom-font.png", func(t *testing.T) {
+		pi.Reset()
+		pi.Resources = fstest.MapFS{
+			"custom-font.png": &fstest.MapFile{Data: customFontPng},
+		}
+		// when
+		err := pi.Boot()
+		// then
+		require.NoError(t, err)
+		assert.Equal(t, uint8(0xf), pi.CustomFont.Data[0])
+	})
+
 	t.Run("should reset draw state", func(t *testing.T) {
 		pi.Reset()
 		require.NoError(t, pi.Boot())

print.go

@@ -6,7 +6,9 @@ package pi
 import (
 	"bytes"
 	_ "embed"
+	"errors"
 	"fmt"
+	"io/fs"
 
 	"github.com/elgopher/pi/image"
 	"github.com/elgopher/pi/internal/font"
@@ -18,6 +20,12 @@ var systemFont = Font{
 	Height:       6,
 }
 
+var CustomFont = Font{
+	Width:        4,
+	WidthSpecial: 8,
+	Height:       6,
+}
+
 //go:embed internal/system-font.png
 var systemFontPNG []byte
 
@@ -96,15 +104,15 @@ func (f Font) printRune(r rune, sx, sy int, color byte) int {
 	}
 }
 
-// loadFontData loads font-sheet (png image) and converts
+// LoadFontData loads font-sheet (png image) and converts
 // it to font data. Image must be 128x128. Each char is 8x8.
 // Char 0 is in the top-left corner. Char 1 to the right.
 //
 // This function can be used if you want to use 3rd font:
 //
 // myFont := pi.Font{Width:4, WidthSpecial:8,Height: 8}
-// pi.loadFontData(png, myFont.Data[:])
-func loadFontData(png []byte, out []byte) error {
+// pi.LoadFontData(png, myFont.Data[:])
+func LoadFontData(png []byte, out []byte) error {
 	img, err := image.DecodePNG(bytes.NewReader(png))
 	if err != nil {
 		return fmt.Errorf("decoding font failed: %w", err)
@@ -117,6 +125,19 @@ func loadFontData(png []byte, out []byte) error {
 	return nil
 }
 
+func loadCustomFont(resources fs.ReadFileFS) error {
+	fileContents, err := resources.ReadFile("custom-font.png")
+	if errors.Is(err, fs.ErrNotExist) {
+		return nil
+	}
+
+	if err != nil {
+		return fmt.Errorf("error loading custom-font.png file: %w", err)
+	}
+
+	return LoadFontData(fileContents, CustomFont.Data[:])
+}
+
 // Print prints text on the screen using system font. It takes into consideration
 // clipping region and camera position.
 //

print_test.go

@@ -145,3 +145,30 @@ func assertScreenEqual(t *testing.T, file string) {
 		fmt.Println("Screenshot taken", screenshot)
 	}
 }
+
+//go:embed internal/testimage/print/custom-font.png
+var customFontPng []byte
+
+//go:embed internal/testimage/print/custom-font-too-small.png
+var customFontTooSmall []byte
+
+func TestLoadFontData(t *testing.T) {
+	t.Run("should return error when font png is invalid", func(t *testing.T) {
+		font := pi.Font{}
+		err := pi.LoadFontData(make([]byte, 0), font.Data[:])
+		require.Error(t, err)
+	})
+
+	t.Run("should return error when png is valid but too small", func(t *testing.T) {
+		font := pi.Font{}
+		err := pi.LoadFontData(customFontTooSmall, font.Data[:])
+		require.Error(t, err)
+	})
+
+	t.Run("should decode png file into font data", func(t *testing.T) {
+		font := pi.Font{}
+		err := pi.LoadFontData(customFontPng, font.Data[:])
+		require.NoError(t, err)
+		assert.Equal(t, byte(0b00001111), font.Data[0])
+	})
+}