mirror of
https://github.com/ivanizag/izapple2.git
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63 lines
1.5 KiB
Go
63 lines
1.5 KiB
Go
package screen
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import (
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"image"
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"image/color"
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)
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const (
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hiResWidth = 280
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hiResLineBytes = hiResWidth / 7
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hiResHeight = 192
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hiResHeightMixed = 160
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)
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func snapshotHiRes(vs VideoSource, isSecondPage bool, light color.Color) *image.RGBA {
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data := vs.GetVideoMemory(isSecondPage, false)
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return renderHiRes(data, light)
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}
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func getHiResLineOffset(line int) uint16 {
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// See "Understanding the Apple II", page 5-14
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// http://www.applelogic.org/files/UNDERSTANDINGTHEAII.pdf
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section := line >> 6 // Top, middle and bottom
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outerEighth := (line >> 3) & 0x07
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innerEighth := line & 0x07
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return uint16(section*40 + outerEighth*0x80 + innerEighth*0x400)
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}
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func renderHiRes(data []uint8, light color.Color) *image.RGBA {
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// As described in "Undertanding the Apple II", with half pixel shifts
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size := image.Rect(0, 0, 2*hiResWidth, hiResHeight)
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img := image.NewRGBA(size)
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for y := 0; y < hiResHeight; y++ {
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offset := getHiResLineOffset(y)
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bytes := data[offset : offset+hiResLineBytes]
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x := 0
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var previousColour color.Color = color.Black
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for _, b := range bytes {
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shifted := b>>7 == 1
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for j := uint(0); j < 7; j++ {
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bit := (b >> j) & 1
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colour := light
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if bit == 0 {
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colour = color.Black
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}
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if shifted {
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// "The general rule of all these HIRES interference patterns is that delayed extends
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// undelayed, and undelayed cuts off delayed"
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img.Set(x, y, previousColour)
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} else {
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img.Set(x, y, colour)
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}
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img.Set(x+1, y, colour)
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previousColour = colour
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x += 2
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}
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}
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}
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return img
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}
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