Don't allocate when drawing by reusing glyp rend buffer

glyphs/glyphs.go

@@ -13,6 +13,9 @@ import (
 	"github.com/golang/freetype/truetype"
 )
 
+const floatsPerGlyph = 11
+const maxGlyphsPerBatch = 16384
+
 type GlyphRend struct {
 	Atlas    *FontAtlas
 	AtlasTex *assets.Texture
@@ -22,7 +25,13 @@ type GlyphRend struct {
 	GlyphMat     *materials.Material
 
 	GlyphCount int32
-	GlyphVBO   []float32
+	//NOTE: Because of the sad realities (bugs?) of CGO, passing an array in a struct
+	//to C explodes (Go pointer to Go pointer error) even though passing the same array
+	//allocated inside the function is fine (Go potentially can't detect what's happening properly).
+	//
+	//Luckily slices still work, so for now we will use our slice as an array (no appending)
+	GlyphVBO []float32
+	// GlyphVBO [floatsPerGlyph * maxGlyphsPerBatch]float32
 
 	ScreenWidth  int32
 	ScreenHeight int32
@@ -43,13 +52,11 @@ func (gr *GlyphRend) DrawTextOpenGLAbs(text string, screenPos *gglm.Vec3, color
 
 	//Prepass to pre-allocate the buffer
 	rs := []rune(text)
-	const floatsPerGlyph = 18
 
 	// startPos := screenPos.Clone()
 	pos := screenPos.Clone()
 	advanceF32 := float32(gr.Atlas.Advance)
 	lineHeightF32 := float32(gr.Atlas.LineHeight)
-	instancedData := make([]float32, 0, len(rs)*floatsPerGlyph) //This a larger approximation than needed because we don't count spaces etc
 	for i := 0; i < len(rs); i++ {
 
 		r := rs[i]
@@ -62,7 +69,6 @@ func (gr *GlyphRend) DrawTextOpenGLAbs(text string, screenPos *gglm.Vec3, color
 			pos.SetX(pos.X() + advanceF32)
 			continue
 		}
-		gr.GlyphCount++
 
 		scale := gglm.NewVec2(advanceF32, lineHeightF32)
 
@@ -73,17 +79,36 @@ func (gr *GlyphRend) DrawTextOpenGLAbs(text string, screenPos *gglm.Vec3, color
 		drawPos.SetX(drawPos.X())
 		drawPos.SetY(drawPos.Y() - g.Descent)
 
-		instancedData = append(instancedData, []float32{
+		//Add the glyph information to the vbo
-			g.U, g.V,
+		startIndex := gr.GlyphCount * floatsPerGlyph
-			color.R(), color.G(), color.B(), color.A(), //Color
-			roundF32(drawPos.X()), roundF32(drawPos.Y()), drawPos.Z(), //Model pos
-			scale.X(), scale.Y(), //Model scale
-		}...)
 
+		//UV
+		gr.GlyphVBO[startIndex+0] = g.U
+		gr.GlyphVBO[startIndex+1] = g.V
+
+		//Color
+		gr.GlyphVBO[startIndex+2] = color.R()
+		gr.GlyphVBO[startIndex+3] = color.G()
+		gr.GlyphVBO[startIndex+4] = color.B()
+		gr.GlyphVBO[startIndex+5] = color.A()
+
+		//Model Pos
+		gr.GlyphVBO[startIndex+6] = roundF32(drawPos.X())
+		gr.GlyphVBO[startIndex+7] = roundF32(drawPos.Y())
+		gr.GlyphVBO[startIndex+8] = drawPos.Z()
+
+		//Model Scale
+		gr.GlyphVBO[startIndex+9] = scale.X()
+		gr.GlyphVBO[startIndex+10] = scale.Y()
+
+		gr.GlyphCount++
 		pos.SetX(pos.X() + advanceF32)
-	}
 
-	gr.GlyphVBO = append(gr.GlyphVBO, instancedData...)
+		//If we fill the buffer we issue a draw call
+		if gr.GlyphCount == maxGlyphsPerBatch {
+			gr.Draw()
+		}
+	}
 }
 
 func (gr *GlyphRend) Draw() {
@@ -92,14 +117,12 @@ func (gr *GlyphRend) Draw() {
 		return
 	}
 
-	gr.InstancedBuf.SetData(gr.GlyphVBO)
+	gr.InstancedBuf.SetData(gr.GlyphVBO[:gr.GlyphCount*floatsPerGlyph])
 	gr.InstancedBuf.Bind()
 	gr.GlyphMat.Bind()
 
 	gl.DrawElementsInstanced(gl.TRIANGLES, gr.GlyphMesh.Buf.IndexBufCount, gl.UNSIGNED_INT, gl.PtrOffset(0), gr.GlyphCount)
-
 	gr.GlyphCount = 0
-	gr.GlyphVBO = []float32{}
 }
 
 //SetFace updates the underlying font atlas used by the glyph renderer.
@@ -178,7 +201,7 @@ func NewGlyphRend(fontFile string, fontOptions *truetype.Options, screenWidth, s
 
 	gr := &GlyphRend{
 		GlyphCount: 0,
-		GlyphVBO:   make([]float32, 0),
+		GlyphVBO:   make([]float32, floatsPerGlyph*maxGlyphsPerBatch),
 	}
 
 	//Create glyph mesh

go.mod

@@ -4,7 +4,7 @@ go 1.18
 
 require (
 	github.com/bloeys/gglm v0.41.10
-	github.com/bloeys/nmage v0.12.12
+	github.com/bloeys/nmage v0.12.13
 	github.com/go-gl/gl v0.0.0-20211025173605-bda47ffaa784
 	github.com/golang/freetype v0.0.0-20170609003504-e2365dfdc4a0
 	github.com/veandco/go-sdl2 v0.4.10

go.sum

@@ -4,6 +4,8 @@ github.com/bloeys/gglm v0.41.10 h1:R9FMiI+VQVXAI+vDwCB7z9xqzy5VAR1657u8TQTDNKA=
 github.com/bloeys/gglm v0.41.10/go.mod h1:qwJQ0WzV191wAMwlGicbfbChbKoSedMk7gFFX6GnyOk=
 github.com/bloeys/nmage v0.12.12 h1:LeMR6NI+yMqxAZecdz7lOT1re4CWAVd1wDeJFK77+pI=
 github.com/bloeys/nmage v0.12.12/go.mod h1:chDDenktiDvAG4BoFYNq1n8nACpbQ6/RFuCgCGmDxh4=
+github.com/bloeys/nmage v0.12.13 h1:xvoaMAdHNnVif7LCaQkYR7jewXDZa9B1iV7IdG39dgc=
+github.com/bloeys/nmage v0.12.13/go.mod h1:chDDenktiDvAG4BoFYNq1n8nACpbQ6/RFuCgCGmDxh4=
 github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/go-gl/gl v0.0.0-20211025173605-bda47ffaa784 h1:1Zi56D0LNfvkzM+BdoxKryvUEdyWO7LP8oRT+oSYJW0=

main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"math/rand"
 
 	"github.com/bloeys/gglm/gglm"
 	"github.com/bloeys/nmage/engine"
@@ -9,6 +10,7 @@ import (
 	"github.com/bloeys/nmage/materials"
 	"github.com/bloeys/nmage/meshes"
 	"github.com/bloeys/nmage/renderer/rend3dgl"
+	"github.com/bloeys/nmage/timing"
 	nmageimgui "github.com/bloeys/nmage/ui/imgui"
 	"github.com/bloeys/nterm/glyphs"
 	"github.com/go-gl/gl/v4.1-core/gl"
@@ -154,20 +156,47 @@ func (p *program) Update() {
 	if input.KeyClicked(sdl.K_SPACE) {
 		p.shouldDrawGrid = !p.shouldDrawGrid
 	}
+
+	fmt.Println("FPS:", int(timing.GetAvgFPS()), "; Draws per frame:", charsPerFrame/16384)
 }
 
+const charsPerFrame = 100_000
+
 var xOff float32 = 0
 var yOff float32 = 0
 
+var r = rand.Float32()
+var g = rand.Float32()
+var b = rand.Float32()
+
 func (p *program) Render() {
 
+	const colorSpd = 0.005
 	defer p.GlyphRend.Draw()
 
-	textColor := gglm.NewVec4(1, 1, 1, 1)
+	r += colorSpd
-	// p.GlyphRend.DrawTextOpenGL("y", gglm.NewVec3(0+xOff, 0+yOff, 0), textColor)
+	if r > 1 {
-	// p.GlyphRend.DrawTextOpenGL("A\np-+_; This is", gglm.NewVec3(0.3+xOff, 0.5+yOff, 0), textColor)
+		r = 0
-	// p.GlyphRend.DrawTextOpenGLAbs("Hello there, friend.\nABCDEFGHIJKLMNOPQRSTUVWXYZ", gglm.NewVec3(0, 0, 0), textColor)
+	}
-	p.GlyphRend.DrawTextOpenGLAbs(" ijojo\n\n Hello there, friend|. pq?\n ABCDEFGHIJKLMNOPQRSTUVWXYZ", gglm.NewVec3(xOff, float32(p.GlyphRend.Atlas.LineHeight)*5+yOff, 0), textColor)
+
+	g += colorSpd
+	if g > 1 {
+		g = 0
+	}
+
+	b += colorSpd
+	if b > 1 {
+		b = 0
+	}
+
+	textColor := gglm.NewVec4(r, g, b, 1)
+
+	str := " ijojo\n\n Hello there, friend|. pq?\n ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+	strLen := len(str)
+
+	for i := 0; i < charsPerFrame/strLen; i++ {
+		p.GlyphRend.DrawTextOpenGLAbs(str, gglm.NewVec3(xOff, float32(p.GlyphRend.Atlas.LineHeight)*5+yOff, 0), textColor)
+	}
 
 	if p.shouldDrawGrid {
 		p.drawGrid()