78 lines
1.9 KiB
Go
78 lines
1.9 KiB
Go
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package apple2
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import (
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"image"
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"image/color"
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"time"
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)
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const (
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charWidth = 7
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charHeight = 8
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textColumns = 40
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textLines = 24
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textPage1Address = uint16(0x0400)
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textPage2Address = uint16(0x0800)
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graphWidth = 280
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graphHeight = 192
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graphPage1Address = uint16(0x2000)
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graphPage2Address = uint16(0x4000)
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)
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func getTextCharOffset(col int, line int) uint16 {
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// See "Understanding the Apple II", page 5-10
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// http://www.applelogic.org/files/UNDERSTANDINGTHEAII.pdf
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section := line / 8 // Top, middle and bottom
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eigth := line % 8
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return uint16(section*40 + eigth*0x80 + col)
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}
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func getTextChar(a *Apple2, col int, line int, page int) uint8 {
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address := textPage1Address
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if page == 1 {
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address = textPage2Address
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}
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address += getTextCharOffset(col, line)
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return a.mmu.internalPeek(address)
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}
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func snapshotTextMode(a *Apple2, page int) *image.RGBA {
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// Color for typical Apple ][ period green phosphor monitors
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// See: https://superuser.com/questions/361297/what-colour-is-the-dark-green-on-old-fashioned-green-screen-computer-displays
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p1GreenPhosphorColor := color.RGBA{65, 255, 0, 255}
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// Flash mode is 2Hz
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isFlashedFrame := time.Now().Nanosecond() > (1 * 1000 * 1000 * 1000 / 2)
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width := textColumns * charWidth
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height := textLines * charHeight
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size := image.Rect(0, 0, width, height)
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img := image.NewRGBA(size)
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for x := 0; x < width; x++ {
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for y := 0; y < height; y++ {
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line := y / charHeight
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col := x / charWidth
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rowInChar := y % charHeight
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colInChar := x % charWidth
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char := getTextChar(a, col, line, page)
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topBits := char >> 6
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isInverse := topBits == 0
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isFlash := topBits == 1
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pixel := a.cg.getPixel(char, rowInChar, colInChar)
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pixel = pixel != (isInverse || (isFlash && isFlashedFrame))
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var colour color.Color
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if pixel {
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colour = p1GreenPhosphorColor
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} else {
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colour = color.Black
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}
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img.Set(x, y, colour)
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}
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}
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return img
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}
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