apple2-go/video/video.go

package video

import (
	"fmt"
	"image"
	"image/color"
	"mos6502go/mmu"

	"github.com/hajimehoshi/ebiten"
	"github.com/hajimehoshi/ebiten/ebitenutil"
)

const (
	screenSizeFactor = 1     // Factor by which the whole screen is resized
	textVideoMemory  = 0x400 // Base location of page 1 text video memory
	flashFrames      = 11    // Number of frames when FLASH mode is toggled
)

var (
	charMap      *ebiten.Image
	flashCounter int
	flashOn      bool
	loresSquares [16]*ebiten.Image
	ShowFPS      bool
)

func Init() {
	var err error
	charMap, _, err = ebitenutil.NewImageFromFile("video/pr-latin1.png", ebiten.FilterNearest)
	if err != nil {
		panic(err)
	}

	for i := 0; i < 16; i++ {
		loresSquares[i], err = ebiten.NewImage(7, 4, ebiten.FilterNearest)
		if err != nil {
			panic(err)
		}
	}

	// From
	// https://mrob.com/pub/xapple2/colors.html
	// https://archive.org/details/IIgs_2523063_Master_Color_Values

	alpha := uint8(0xff)
	loresSquares[0x00].Fill(color.NRGBA{0, 0, 0, alpha})
	loresSquares[0x01].Fill(color.NRGBA{221, 0, 51, alpha})
	loresSquares[0x02].Fill(color.NRGBA{0, 0, 153, alpha})
	loresSquares[0x03].Fill(color.NRGBA{221, 34, 221, alpha})
	loresSquares[0x04].Fill(color.NRGBA{0, 119, 34, alpha})
	loresSquares[0x05].Fill(color.NRGBA{85, 85, 85, alpha})
	loresSquares[0x06].Fill(color.NRGBA{34, 34, 255, alpha})
	loresSquares[0x07].Fill(color.NRGBA{102, 170, 255, alpha})
	loresSquares[0x08].Fill(color.NRGBA{136, 85, 0, alpha})
	loresSquares[0x09].Fill(color.NRGBA{255, 102, 0, alpha})
	loresSquares[0x0A].Fill(color.NRGBA{170, 170, 170, alpha})
	loresSquares[0x0B].Fill(color.NRGBA{255, 153, 136, alpha})
	loresSquares[0x0C].Fill(color.NRGBA{17, 221, 0, alpha})
	loresSquares[0x0D].Fill(color.NRGBA{255, 255, 0, alpha})
	loresSquares[0x0E].Fill(color.NRGBA{68, 255, 153, alpha})
	loresSquares[0x0F].Fill(color.NRGBA{255, 255, 255, alpha})

	ShowFPS = false
}

func drawText(screen *ebiten.Image, x int, y int, value uint8, flashOn bool) error {
	inverted := false

	if (value & 0xc0) == 0 {
		inverted = true
	} else if (value & 0x80) == 0 {
		value = value & 0x3f
		inverted = flashOn
	}

	if !inverted {
		value = value & 0x7f
	}

	if value < 0x20 {
		value += 0x40
	}

	op := &ebiten.DrawImageOptions{}
	op.GeoM.Scale(screenSizeFactor, screenSizeFactor)
	op.GeoM.Translate(screenSizeFactor*7*float64(x), screenSizeFactor*8*float64(y))

	fontRow := value % 16
	fontCol := value / 16
	var fontX = (int)(15 + fontCol*12)
	var fontY = (int)(32 + fontRow*11)
	r := image.Rect(fontX, fontY, fontX+7, fontY+8)
	op.SourceRect = &r

	if !inverted {
		op.ColorM.Scale(-1, -1, -1, 1)
		op.ColorM.Translate(1, 1, 1, 0)
	}

	op.ColorM.Scale(0.20, 0.75, 0.20, 1)

	return screen.DrawImage(charMap, op)
}

func drawLores(screen *ebiten.Image, x int, y int, value uint8) error {
	var values [2]uint8 = [2]uint8{value & 0xf, value >> 4}

	for i := 0; i < 2; i++ {
		op := &ebiten.DrawImageOptions{}
		op.GeoM.Scale(screenSizeFactor, screenSizeFactor)
		op.GeoM.Translate(screenSizeFactor*7*float64(x), screenSizeFactor*8*float64(y)+float64(i)*4)
		if err := screen.DrawImage(loresSquares[values[i]], op); err != nil {
			return err
		}
	}

	return nil
}

func DrawScreen(screen *ebiten.Image) error {
	topHalfIsLowRes := !mmu.VideoState.TextMode
	bottomHalfIsLowRes := !mmu.VideoState.TextMode && !mmu.VideoState.Mixed

	flashCounter--
	if flashCounter < 0 {
		flashCounter = flashFrames
		flashOn = !flashOn
	}

	if ebiten.IsRunningSlowly() {
		return nil
	}

	for y := 0; y < 24; y++ {
		base := 128*(y%8) + 40*(y/8)
		for x := 0; x < 40; x++ {
			offset := textVideoMemory + base + x
			value := mmu.PageTable[offset>>8][offset&0xff]

			topHalf := y < 20
			if (topHalf && topHalfIsLowRes) || (!topHalf && bottomHalfIsLowRes) {
				if err := drawLores(screen, x, y, value); err != nil {
					return err
				}
			} else {
				if err := drawText(screen, x, y, value, flashOn); err != nil {
					return err
				}
			}

		}
	}

	if ShowFPS {
		msg := fmt.Sprintf(`FPS: %0.2f`, ebiten.CurrentFPS())
		ebitenutil.DebugPrint(screen, msg)
	}

	return nil
}