font.go

package video

import (
	"fmt"
	"image"
	"image/draw"
	"io"
	"io/ioutil"
	"os"

	"github.com/go-gl/gl/v2.1/gl"
	"github.com/golang/freetype"
	"github.com/golang/freetype/truetype"
	"golang.org/x/image/font"
	"golang.org/x/image/math/fixed"
)

type character struct {
	x, y     int
	width    int // Glyph width
	height   int // Glyph height
	advance  int // Glyph advance
	bearingH int // Glyph bearing horizontal
	bearingV int // Glyph bearing vertical
}

// Direction represents the direction in which strings should be rendered.
type Direction uint8

// Known directions.
const (
	LeftToRight Direction = iota // E.g.: Latin
	RightToLeft                  // E.g.: Arabic
	TopToBottom                  // E.g.: Chinese
)

// A Font allows rendering of text to an OpenGL context.
type Font struct {
	fontChar    []*character
	vao         uint32
	vbo         uint32
	program     uint32
	textureID   uint32 // Holds the glyph texture id.
	color       Color
	atlasWidth  float32
	atlasHeight float32
}

type point [4]float32

func max(a, b float32) float32 {
	if a > b {
		return a
	}
	return b
}

// LoadTrueTypeFont builds a set of textures based on a ttf files gylphs
func LoadTrueTypeFont(program uint32, r io.Reader, scale int32, low, high rune, dir Direction) (*Font, error) {
	data, err := ioutil.ReadAll(r)
	if err != nil {
		return nil, err
	}

	// Read the truetype font.
	ttf, err := truetype.Parse(data)
	if err != nil {
		return nil, err
	}

	// Make Font stuct type
	f := new(Font)
	f.fontChar = make([]*character, 0, high-low+1)
	f.program = program                       // Set shader program
	f.SetColor(Color{R: 1, G: 1, B: 1, A: 1}) // Set default white

	// Create new face
	ttfFace := truetype.NewFace(ttf, &truetype.Options{
		Size:    float64(scale),
		DPI:     72,
		Hinting: font.HintingFull,
	})

	var lineHeight float32
	f.atlasWidth = 1024
	f.atlasHeight = 1024
	for ch := low; ch <= high; ch++ {
		gBnd, _, ok := ttfFace.GlyphBounds(ch)
		if !ok {
			return nil, fmt.Errorf("ttf face glyphBounds error")
		}
		gh := int32((gBnd.Max.Y - gBnd.Min.Y) >> 6)
		lineHeight = max(lineHeight, float32(gh))
	}

	// Create image to draw glyph
	fg, bg := image.White, image.Black
	rect := image.Rect(0, 0, int(f.atlasWidth), int(f.atlasHeight))
	rgba := image.NewRGBA(rect)
	draw.Draw(rgba, rgba.Bounds(), bg, image.Point{}, draw.Src)

	margin := 4
	x := margin
	y := margin

	// Make each gylph
	for ch := low; ch <= high; ch++ {
		char := new(character)

		gBnd, gAdv, ok := ttfFace.GlyphBounds(ch)
		if !ok {
			return nil, fmt.Errorf("ttf face glyphBounds error")
		}

		gh := int32((gBnd.Max.Y - gBnd.Min.Y) >> 6)
		gw := int32((gBnd.Max.X - gBnd.Min.X) >> 6)

		// If gylph has no dimensions set to a max value
		if gw == 0 || gh == 0 {
			gBnd = ttf.Bounds(fixed.Int26_6(scale))
			gw = int32((gBnd.Max.X - gBnd.Min.X) >> 6)
			gh = int32((gBnd.Max.Y - gBnd.Min.Y) >> 6)

			// Above can sometimes yield 0 for font smaller than 48pt, 1 is minimum
			if gw == 0 || gh == 0 {
				gw = 1
				gh = 1
			}
		}

		// The glyph's ascent and descent equal -bounds.Min.Y and +bounds.Max.Y.
		gAscent := int(-gBnd.Min.Y) >> 6
		gdescent := int(gBnd.Max.Y) >> 6

		// Set w,h and adv, bearing V and bearing H in char
		char.x = x
		char.y = y
		char.width = int(gw)
		char.height = int(gh)
		char.advance = int(gAdv)
		char.bearingV = gdescent
		char.bearingH = (int(gBnd.Min.X) >> 6)

		clip := image.Rect(x, y, x+int(gw), y+int(gh))

		// Create a freetype context for drawing
		c := freetype.NewContext()
		c.SetDPI(72)
		c.SetFont(ttf)
		c.SetFontSize(float64(scale))
		c.SetClip(clip)
		c.SetDst(rgba)
		c.SetSrc(fg)
		c.SetHinting(font.HintingFull)

		// Set the glyph dot
		px := 0 - (int(gBnd.Min.X) >> 6) + x
		py := (gAscent) + y
		pt := freetype.Pt(px, py)

		x += int(gw) + margin
		if x+int(gw)+margin > int(f.atlasWidth) {
			x = 0
			y += int(lineHeight) + margin
		}

		// Draw the text from mask to image
		_, err = c.DrawString(string(ch), pt)
		if err != nil {
			return nil, err
		}

		// Add char to fontChar list
		f.fontChar = append(f.fontChar, char)
	}

	// Generate texture
	gl.GenTextures(1, &f.textureID)
	gl.BindTexture(gl.TEXTURE_2D, f.textureID)
	gl.PixelStorei(gl.UNPACK_ALIGNMENT, 1)
	gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR_MIPMAP_LINEAR)
	gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR)

	gl.TexImage2D(gl.TEXTURE_2D, 0, gl.RGBA, int32(rgba.Rect.Dx()), int32(rgba.Rect.Dy()), 0, gl.RGBA, gl.UNSIGNED_BYTE, gl.Ptr(rgba.Pix))

	gl.GenerateMipmap(gl.TEXTURE_2D)
	gl.BindTexture(gl.TEXTURE_2D, 0)

	// Configure VAO/VBO for texture quads
	genVertexArrays(1, &f.vao)
	gl.GenBuffers(1, &f.vbo)
	bindVertexArray(f.vao)
	gl.BindBuffer(gl.ARRAY_BUFFER, f.vbo)

	vertAttrib := uint32(gl.GetAttribLocation(f.program, gl.Str("vert\x00")))
	gl.EnableVertexAttribArray(vertAttrib)
	gl.VertexAttribPointer(vertAttrib, 2, gl.FLOAT, false, 4*4, gl.PtrOffset(0))

	texCoordAttrib := uint32(gl.GetAttribLocation(f.program, gl.Str("vertTexCoord\x00")))
	gl.EnableVertexAttribArray(texCoordAttrib)
	gl.VertexAttribPointer(texCoordAttrib, 2, gl.FLOAT, false, 4*4, gl.PtrOffset(2*4))

	gl.BindBuffer(gl.ARRAY_BUFFER, 0)
	bindVertexArray(0)

	return f, nil
}

// LoadFont loads the specified font at the given scale.
func LoadFont(file string, scale int32, windowWidth int, windowHeight int) (*Font, error) {
	fd, err := os.Open(file)
	if err != nil {
		return nil, err
	}
	defer fd.Close()

	// Configure the default font vertex and fragment shaders
	program, err := newProgram(fontVertexShader, fontFragmentShader)
	if err != nil {
		panic(err)
	}

	// Activate corresponding render state
	gl.UseProgram(program)

	// Set screen resolution
	resUniform := gl.GetUniformLocation(program, gl.Str("resolution\x00"))
	gl.Uniform2f(resUniform, float32(windowWidth), float32(windowHeight))

	return LoadTrueTypeFont(program, fd, scale, 32, 256, LeftToRight)
}

// SetColor allows you to set the text color to be used when you draw the text
func (f *Font) SetColor(c Color) {
	f.color = c
}

// UpdateResolution passes the new framebuffer size to the font shader
func (f *Font) UpdateResolution(windowWidth int, windowHeight int) {
	gl.UseProgram(f.program)
	resUniform := gl.GetUniformLocation(f.program, gl.Str("resolution\x00"))
	gl.Uniform2f(resUniform, float32(windowWidth), float32(windowHeight))
	gl.UseProgram(0)
}

// Printf draws a string to the screen, takes a list of arguments like printf
func (f *Font) Printf(x, y float32, scale float32, fs string, argv ...interface{}) error {
	indices := []rune(fmt.Sprintf(fs, argv...))

	if len(indices) == 0 {
		return nil
	}

	lowChar := rune(32)

	// Setup blending mode
	gl.Enable(gl.BLEND)
	gl.BlendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA)

	// Activate corresponding render state
	gl.UseProgram(f.program)
	// Set text color
	gl.Uniform4f(gl.GetUniformLocation(f.program, gl.Str("textColor\x00")), f.color.R, f.color.G, f.color.B, f.color.A)

	var coords []point

	// Iterate through all characters in string
	for i := range indices {
		// Get rune
		runeIndex := indices[i]

		var ch *character
		// Skip runes that are not in font chacter range
		if int(runeIndex)-int(lowChar) > len(f.fontChar) || runeIndex < lowChar {
			// Print a ?
			ch = f.fontChar[int(rune('?'))-int(lowChar)]
		} else {
			// Find rune in fontChar list
			ch = f.fontChar[runeIndex-lowChar]
		}

		// Calculate position and size for current rune
		xpos := x - 1 + float32(ch.bearingH)*scale
		ypos := y - 2 - float32(ch.height-ch.bearingV)*scale
		w := float32(ch.width+2) * scale
		h := float32(ch.height+2) * scale

		// Set quad positions
		var x1 = xpos
		var x2 = xpos + w
		var y1 = ypos
		var y2 = ypos + h

		coords = append(coords, point{x1, y1, float32(ch.x-1) / f.atlasWidth, float32(ch.y-1) / f.atlasHeight})
		coords = append(coords, point{x2, y1, float32(ch.x+ch.width+1) / f.atlasWidth, float32(ch.y-1) / f.atlasHeight})
		coords = append(coords, point{x1, y2, float32(ch.x-1) / f.atlasWidth, float32(ch.y+ch.height+1) / f.atlasHeight})
		coords = append(coords, point{x2, y1, float32(ch.x+ch.width+1) / f.atlasWidth, float32(ch.y-1) / f.atlasHeight})
		coords = append(coords, point{x1, y2, float32(ch.x-1) / f.atlasWidth, float32(ch.y+ch.height+1) / f.atlasHeight})
		coords = append(coords, point{x2, y2, float32(ch.x+ch.width+1) / f.atlasWidth, float32(ch.y+ch.height+1) / f.atlasHeight})

		// Now advance cursors for next glyph (note that advance is number of 1/64 pixels)
		x += float32((ch.advance >> 6)) * scale // Bitshift by 6 to get value in pixels (2^6 = 64 (divide amount of 1/64th pixels by 64 to get amount of pixels))
	}

	bindVertexArray(f.vao)
	gl.ActiveTexture(gl.TEXTURE0)
	gl.BindTexture(gl.TEXTURE_2D, f.textureID)
	gl.BindBuffer(gl.ARRAY_BUFFER, f.vbo)
	gl.BufferData(gl.ARRAY_BUFFER, len(coords)*16, gl.Ptr(coords), gl.DYNAMIC_DRAW)
	gl.DrawArrays(gl.TRIANGLES, 0, int32(len(coords)))
	bindVertexArray(0)
	gl.BindTexture(gl.TEXTURE_2D, 0)
	gl.UseProgram(0)
	gl.Disable(gl.BLEND)

	return nil
}

// Width returns the width of a piece of text in pixels
func (f *Font) Width(scale float32, fs string, argv ...interface{}) float32 {
	var width float32

	indices := []rune(fmt.Sprintf(fs, argv...))

	if len(indices) == 0 {
		return 0
	}

	lowChar := rune(32)

	// Iterate through all characters in string
	for i := range indices {

		// Get rune
		runeIndex := indices[i]

		// Skip runes that are not in font chacter range
		if int(runeIndex)-int(lowChar) > len(f.fontChar) || runeIndex < lowChar {
			fmt.Printf("%c %d\n", runeIndex, runeIndex)
			continue
		}

		// Find rune in fontChar list
		ch := f.fontChar[runeIndex-lowChar]

		// Now advance cursors for next glyph (note that advance is number of 1/64 pixels)
		width += float32((ch.advance >> 6)) * scale // Bitshift by 6 to get value in pixels (2^6 = 64 (divide amount of 1/64th pixels by 64 to get amount of pixels))

	}

	return width
}