ebitenutil/debugprint.go: Using triangles instead of images

debugprint.go

// Copyright 2014 Hajime Hoshi
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package ebitenutil

import (
	"image"

	"github.com/hajimehoshi/ebiten/v2"
	"github.com/hajimehoshi/ebiten/v2/ebitenutil/internal/assets"
)

var (
	debugPrintTextImage     = ebiten.NewImageFromImage(assets.CreateTextImage())
	debugPrintTextSubImages = map[rune]*ebiten.Image{}
)

// DebugPrint draws the string str on the image on left top corner.
//
// The available runes are in U+0000 to U+00FF, which is C0 Controls and Basic Latin and C1 Controls and Latin-1 Supplement.
func DebugPrint(image *ebiten.Image, str string) {
	DebugPrintAt(image, str, 0, 0)
}

// DebugPrintAt draws the string str on the image at (x, y) position.
//
// The available runes are in U+0000 to U+00FF, which is C0 Controls and Basic Latin and C1 Controls and Latin-1 Supplement.
func DebugPrintAt(image *ebiten.Image, str string, x, y int) {
	drawDebugText(image, str, x+1, y+1, true)
	drawDebugText(image, str, x, y, false)
}

func drawDebugText(rt *ebiten.Image, str string, ox, oy int, shadow bool) {
	op := &ebiten.DrawImageOptions{}
	if shadow {
		op.ColorM.Scale(0, 0, 0, 0.5)
	}
	x := 0
	y := 0
	w, _ := debugPrintTextImage.Size()
	for _, c := range str {
		const (
			cw = assets.CharWidth
			ch = assets.CharHeight
		)
		if c == '\n' {
			x = 0
			y += ch
			continue
		}
		s, ok := debugPrintTextSubImages[c]
		if !ok {
			n := w / cw
			sx := (int(c) % n) * cw
			sy := (int(c) / n) * ch
			s = debugPrintTextImage.SubImage(image.Rect(sx, sy, sx+cw, sy+ch)).(*ebiten.Image)
			debugPrintTextSubImages[c] = s
		}
		op.GeoM.Reset()
		op.GeoM.Translate(float64(x), float64(y))
		op.GeoM.Translate(float64(ox+1), float64(oy))
		rt.DrawImage(s, op)
		x += cw
	}
}

func DebugPrintWithTrianglesAt(image *ebiten.Image, str string, x, y int) {
	drawDebugTextWithTriangles(image, str, x+1, y+1, true)
	drawDebugTextWithTriangles(image, str, x, y, false)
}

var boxIndices = [6]uint16{0, 1, 2, 1, 2, 3}

func drawDebugTextWithTriangles(rt *ebiten.Image, str string, ox, oy int, shadow bool) {
	op := &ebiten.DrawTrianglesOptions{}
	if shadow {
		op.ColorM.Scale(0, 0, 0, 0.5)
	}

	x := 0
	y := 0
	w, _ := debugPrintTextImage.Size()
	vertices := make([]ebiten.Vertex, 0, len(str)*4)
	indices := make([]uint16, 0, len(str)*6)
	for i, c := range str {
		const (
			cw = assets.CharWidth
			ch = assets.CharHeight
		)
		if c == '\n' {
			x = 0
			y += ch
			continue
		}

		n := w / cw
		sx := (int(c) % n) * cw
		sy := (int(c) / n) * ch
		vertices = append(vertices, []ebiten.Vertex{
			{
				DstX:   float32(x + ox + 1),
				DstY:   float32(y + oy),
				SrcX:   float32(sx),
				SrcY:   float32(sy),
				ColorR: 1,
				ColorG: 1,
				ColorB: 1,
				ColorA: 1,
			},
			{
				DstX:   float32(x + ox + 1 + cw),
				DstY:   float32(y + oy),
				SrcX:   float32(sx + cw),
				SrcY:   float32(sy),
				ColorR: 1,
				ColorG: 1,
				ColorB: 1,
				ColorA: 1,
			},
			{
				DstX:   float32(x + ox + 1),
				DstY:   float32(y + oy + ch),
				SrcX:   float32(sx),
				SrcY:   float32(sy + ch),
				ColorR: 1,
				ColorG: 1,
				ColorB: 1,
				ColorA: 1,
			},
			{
				DstX:   float32(x + ox + 1 + cw),
				DstY:   float32(y + oy + ch),
				SrcX:   float32(sx + cw),
				SrcY:   float32(sy + ch),
				ColorR: 1,
				ColorG: 1,
				ColorB: 1,
				ColorA: 1,
			},
		}...)
		indiceCursor := uint16(i * 4)
		indices = append(indices, []uint16{
			boxIndices[0] + indiceCursor,
			boxIndices[1] + indiceCursor,
			boxIndices[2] + indiceCursor,
			boxIndices[3] + indiceCursor,
			boxIndices[4] + indiceCursor,
			boxIndices[5] + indiceCursor,
		}...)

		x += cw
	}
	rt.DrawTriangles(vertices, indices, debugPrintTextImage, op)
}