izapple2/screenHiRes.go
2020-08-10 20:52:17 +02:00

68 lines
1.6 KiB
Go

package apple2
import (
"image"
"image/color"
)
const (
hiResWidth = 280
hiResLineBytes = hiResWidth / 7
hiResHeight = 192
hiResHeightMixed = 160
hiResPage1Address = uint16(0x2000)
hiResPage2Address = uint16(0x4000)
)
func getHiResLineOffset(line int) uint16 {
// See "Understanding the Apple II", page 5-14
// http://www.applelogic.org/files/UNDERSTANDINGTHEAII.pdf
section := line >> 6 // Top, middle and bottom
outerEighth := (line >> 3) & 0x07
innerEighth := line & 0x07
return uint16(section*40 + outerEighth*0x80 + innerEighth*0x400)
}
func getHiResLine(a *Apple2, line int, isSecondPage bool, auxMem bool) []uint8 {
address := hiResPage1Address
if isSecondPage {
address = hiResPage2Address
}
address += getHiResLineOffset(line)
return a.mmu.getVideoRAM(auxMem).subRange(address, address+hiResLineBytes)
}
func snapshotHiResModeMono(a *Apple2, isSecondPage bool, light color.Color) *image.RGBA {
// As described in "Undertanding the Apple II", with half pixel shifts
size := image.Rect(0, 0, 2*hiResWidth, hiResHeight)
img := image.NewRGBA(size)
for y := 0; y < hiResHeight; y++ {
bytes := getHiResLine(a, y, isSecondPage, false /*auxMem*/)
x := 0
var previousColour color.Color = color.Black
for _, b := range bytes {
shifted := b>>7 == 1
for j := uint(0); j < 7; j++ {
bit := (b >> j) & 1
colour := light
if bit == 0 {
colour = color.Black
}
if shifted {
img.Set(x, y, previousColour)
} else {
img.Set(x, y, colour)
}
img.Set(x+1, y, colour)
previousColour = colour
x += 2
}
}
}
return img
}