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font.go
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font.go
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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.VertexAttribPointerWithOffset(vertAttrib, 2, gl.FLOAT, false, 4*4, 0)
texCoordAttrib := uint32(gl.GetAttribLocation(f.program, gl.Str("vertTexCoord\x00")))
gl.EnableVertexAttribArray(texCoordAttrib)
gl.VertexAttribPointerWithOffset(texCoordAttrib, 2, gl.FLOAT, false, 4*4, 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
}