izapple2/apple2/screenText.go
2019-05-03 21:45:29 +02:00

76 lines
1.7 KiB
Go

package apple2
import (
"image"
"image/color"
"time"
)
const (
charWidth = 7
charHeight = 8
textColumns = 40
textLines = 24
textLinesMix = 4
textPage1Address = uint16(0x0400)
textPage2Address = uint16(0x0800)
)
func getTextCharOffset(col int, line int) uint16 {
// See "Understanding the Apple II", page 5-10
// http://www.applelogic.org/files/UNDERSTANDINGTHEAII.pdf
section := line / 8 // Top, middle and bottom
eigth := line % 8
return uint16(section*40 + eigth*0x80 + col)
}
func getTextChar(a *Apple2, col int, line int, page int) uint8 {
address := textPage1Address
if page == 1 {
address = textPage2Address
}
address += getTextCharOffset(col, line)
return a.mmu.internalPeek(address)
}
func snapshotTextMode(a *Apple2, page int, mixMode bool, light color.Color) *image.RGBA {
// Flash mode is 2Hz
isFlashedFrame := time.Now().Nanosecond() > (1 * 1000 * 1000 * 1000 / 2)
lineStart := 0
if mixMode {
lineStart = textLines - textLinesMix
}
width := textColumns * charWidth
height := (textLines - lineStart) * charHeight
size := image.Rect(0, 0, width, height)
img := image.NewRGBA(size)
for x := 0; x < width; x++ {
for y := 0; y < height; y++ {
line := y/charHeight + lineStart
col := x / charWidth
rowInChar := y % charHeight
colInChar := x % charWidth
char := getTextChar(a, col, line, page)
topBits := char >> 6
isInverse := topBits == 0
isFlash := topBits == 1
pixel := a.cg.getPixel(char, rowInChar, colInChar)
pixel = pixel != (isInverse || (isFlash && isFlashedFrame))
var colour color.Color
if pixel {
colour = light
} else {
colour = color.Black
}
img.Set(x, y, colour)
}
}
return img
}