added support for loading fonts and rendering text (highly unoptimized so far)

canvas.go

@@ -1,6 +1,7 @@
 package canvas
 
 import (
+	"image"
 	"unsafe"
 
 	"github.com/tfriedel6/lm"
@@ -20,6 +21,12 @@ type Canvas struct {
 		lineWidth  float32
 	}
 	path []pathPoint
+	text struct {
+		font   *Font
+		size   float32
+		target *image.RGBA
+		tex    uint32
+	}
 }
 
 type pathPoint struct {

color.go

@@ -7,7 +7,7 @@ import (
 	"strings"
 )
 
-func colorToGL(color color.Color) (r, g, b, a float32) {
+func colorGoToGL(color color.Color) (r, g, b, a float32) {
 	ir, ig, ib, ia := color.RGBA()
 	r = float32(ir) / 65535
 	g = float32(ig) / 65535
@@ -16,6 +16,35 @@ func colorToGL(color color.Color) (r, g, b, a float32) {
 	return
 }
 
+func colorGLToGo(r, g, b, a float32) color.Color {
+	if r < 0 {
+		r = 0
+	} else if r > 1 {
+		r = 1
+	}
+	if g < 0 {
+		g = 0
+	} else if g > 1 {
+		g = 1
+	}
+	if b < 0 {
+		b = 0
+	} else if b > 1 {
+		b = 1
+	}
+	if a < 0 {
+		a = 0
+	} else if a > 1 {
+		a = 1
+	}
+	return color.RGBA{
+		R: uint8(r * 255),
+		G: uint8(g * 255),
+		B: uint8(b * 255),
+		A: uint8(a * 255),
+	}
+}
+
 func parseHexRune(rn rune) (int, bool) {
 	switch {
 	case rn >= '0' && rn <= '9':
@@ -93,7 +122,7 @@ func parseColor(value ...interface{}) (r, g, b, a float32, ok bool) {
 	if len(value) == 1 {
 		switch v := value[0].(type) {
 		case color.Color:
-			r, g, b, a = colorToGL(v)
+			r, g, b, a = colorGoToGL(v)
 			ok = true
 			return
 		case [3]float32:

images.go

@@ -43,6 +43,7 @@ func LoadImage(src interface{}) (*Image, error) {
 func loadImageRGBA(src *image.RGBA) (*Image, error) {
 	img := &Image{w: src.Bounds().Dx(), h: src.Bounds().Dy()}
 	gli.GenTextures(1, &img.tex)
+	gli.ActiveTexture(gl_TEXTURE0)
 	gli.BindTexture(gl_TEXTURE_2D, img.tex)
 	gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MIN_FILTER, gl_LINEAR_MIPMAP_LINEAR)
 	gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MAG_FILTER, gl_LINEAR)
@@ -75,6 +76,7 @@ func loadImageRGBA(src *image.RGBA) (*Image, error) {
 func loadImageGray(src *image.Gray) (*Image, error) {
 	img := &Image{w: src.Bounds().Dx(), h: src.Bounds().Dy()}
 	gli.GenTextures(1, &img.tex)
+	gli.ActiveTexture(gl_TEXTURE0)
 	gli.BindTexture(gl_TEXTURE_2D, img.tex)
 	gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MIN_FILTER, gl_LINEAR_MIPMAP_LINEAR)
 	gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MAG_FILTER, gl_LINEAR)
@@ -107,6 +109,7 @@ func loadImageGray(src *image.Gray) (*Image, error) {
 func loadImageConverted(src image.Image) (*Image, error) {
 	img := &Image{w: src.Bounds().Dx(), h: src.Bounds().Dy()}
 	gli.GenTextures(1, &img.tex)
+	gli.ActiveTexture(gl_TEXTURE0)
 	gli.BindTexture(gl_TEXTURE_2D, img.tex)
 	gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MIN_FILTER, gl_LINEAR_MIPMAP_LINEAR)
 	gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MAG_FILTER, gl_LINEAR)

text.go

@@ -0,0 +1,99 @@
+package canvas
+
+import (
+	"errors"
+	"image"
+	"io/ioutil"
+	"unsafe"
+
+	"github.com/golang/freetype"
+	"github.com/golang/freetype/truetype"
+	"golang.org/x/image/math/fixed"
+)
+
+var fontRenderingContext = freetype.NewContext()
+
+type Font struct {
+	font *truetype.Font
+}
+
+func LoadFont(src interface{}) (*Font, error) {
+	switch v := src.(type) {
+	case *truetype.Font:
+		return &Font{font: v}, nil
+	case string:
+		data, err := ioutil.ReadFile(v)
+		if err != nil {
+			return nil, err
+		}
+		font, err := freetype.ParseFont(data)
+		if err != nil {
+			return nil, err
+		}
+		return &Font{font: font}, nil
+	case []byte:
+		font, err := freetype.ParseFont(v)
+		if err != nil {
+			return nil, err
+		}
+		return &Font{font: font}, nil
+	}
+	return nil, errors.New("Unsupported source type")
+}
+
+func (cv *Canvas) SetFont(font *Font, size float32) {
+	cv.text.font = font
+	cv.text.size = size
+}
+
+func (cv *Canvas) FillText(str string, x, y float32) {
+	cv.activate()
+
+	if cv.text.target == nil || cv.text.target.Bounds().Dx() != cv.w || cv.text.target.Bounds().Dy() != cv.h {
+		if cv.text.tex != 0 {
+			gli.DeleteTextures(1, &cv.text.tex)
+		}
+		cv.text.target = image.NewRGBA(image.Rect(0, 0, cv.w, cv.h))
+		gli.GenTextures(1, &cv.text.tex)
+		gli.ActiveTexture(gl_TEXTURE0)
+		gli.BindTexture(gl_TEXTURE_2D, cv.text.tex)
+		gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MIN_FILTER, gl_NEAREST)
+		gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MAG_FILTER, gl_NEAREST)
+		gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_WRAP_S, gl_CLAMP_TO_EDGE)
+		gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_WRAP_T, gl_CLAMP_TO_EDGE)
+	}
+
+	for i := range cv.text.target.Pix {
+		cv.text.target.Pix[i] = 0
+	}
+
+	fontRenderingContext.SetFont(cv.text.font.font)
+	fontRenderingContext.SetFontSize(float64(cv.text.size))
+	fontRenderingContext.SetSrc(image.NewUniform(colorGLToGo(cv.fill.r, cv.fill.g, cv.fill.b, cv.fill.a)))
+	fontRenderingContext.SetDst(cv.text.target)
+	fontRenderingContext.SetClip(cv.text.target.Bounds())
+	fontRenderingContext.DrawString(str, fixed.Point26_6{X: fixed.Int26_6(x*64 + 0.5), Y: fixed.Int26_6(y*64 + 0.5)})
+
+	gli.BlendFunc(gl_ONE, gl_ONE_MINUS_SRC_ALPHA)
+
+	gli.ActiveTexture(gl_TEXTURE0)
+	gli.BindTexture(gl_TEXTURE_2D, cv.text.tex)
+	gli.TexImage2D(gl_TEXTURE_2D, 0, gl_RGBA, int32(cv.w), int32(cv.h), 0, gl_RGBA, gl_UNSIGNED_BYTE, gli.Ptr(&cv.text.target.Pix[0]))
+
+	gli.UseProgram(tr.id)
+	gli.Uniform1i(tr.image, 0)
+
+	gli.BindBuffer(gl_ARRAY_BUFFER, buf)
+	data := [16]float32{-1, -1, -1, 1, 1, 1, 1, -1, 0, 1, 0, 0, 1, 0, 1, 1}
+	gli.BufferData(gl_ARRAY_BUFFER, len(data)*4, unsafe.Pointer(&data[0]), gl_STREAM_DRAW)
+
+	gli.VertexAttribPointer(tr.vertex, 2, gl_FLOAT, false, 0, nil)
+	gli.VertexAttribPointer(tr.texCoord, 2, gl_FLOAT, false, 0, gli.PtrOffset(8*4))
+	gli.EnableVertexAttribArray(tr.vertex)
+	gli.EnableVertexAttribArray(tr.texCoord)
+	gli.DrawArrays(gl_TRIANGLE_FAN, 0, 4)
+	gli.DisableVertexAttribArray(tr.vertex)
+	gli.DisableVertexAttribArray(tr.texCoord)
+
+	gli.BlendFunc(gl_SRC_ALPHA, gl_ONE_MINUS_SRC_ALPHA)
+}