112 lines
2.6 KiB
Go
112 lines
2.6 KiB
Go
package apple2
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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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loResPixelWidth = charWidth
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loResPixelHeight = charHeight / 2
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loResWidth = textColumns
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loResHeight = textLines * 2
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loResHeightMixed = (textLines - textLinesMix) * 2
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loRes
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loResPage1Address = textPage1Address
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loResPage2Address = textPage2Address
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)
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func getLoResPixel(a *Apple2, x int, y int, page int) uint8 {
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// Each text mode char encodes two pixels
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char := getTextChar(a, x, y/2, page)
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if y%2 == 0 {
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// Top pixel in char
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return char & 0xf
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}
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// Bottom pixel in char
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return char >> 4
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}
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func snapshotLoResModeReferenceColor(a *Apple2, page int, mixedMode bool) *image.RGBA {
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// As defined on "Apple II Reference Manual"
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height := loResHeight
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if mixedMode {
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height = loResHeightMixed
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}
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size := image.Rect(0, 0, loResWidth, height)
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img := image.NewRGBA(size)
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// Lores colors correspond to the NTSC 4 bit patterns reversed
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colorMap := getNTSCColorMap()
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reversedNibble := []uint8{0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15}
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for x := 0; x < loResWidth; x++ {
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for y := 0; y < height; y++ {
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v := getLoResPixel(a, x, y, page)
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img.Set(x, y, colorMap[reversedNibble[v]])
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}
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}
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return img
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}
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func getColorPatterns(light color.Color) [16][16]color.Color {
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/*
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For each lores pixel we have to fill 14 half mono pixels with
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the 4 bits of the color repeated. We will need to shift by 2 bits
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on the odd columns. Lets prepare 14+2 values for each color.
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*/
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var data [16][16]color.Color
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for ci := 0; ci < 16; ci++ {
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for cb := uint8(0); cb < 4; cb++ {
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bit := (ci >> cb) & 1
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var colour color.Color
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if bit == 0 {
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colour = color.Black
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} else {
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colour = light
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}
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for i := uint8(0); i < 4; i++ {
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data[ci][cb+4*i] = colour
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}
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}
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}
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return data
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}
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func snapshotLoResModeMonoShift(a *Apple2, page int, mixedMode bool, light color.Color) *image.RGBA {
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// As described in "Undertanding the Apple II", with half pixel shifts
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height := loResHeight
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if mixedMode {
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height = loResHeightMixed
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}
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size := image.Rect(0, 0, 2*loResWidth*loResPixelWidth, height*loResPixelHeight)
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img := image.NewRGBA(size)
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patterns := getColorPatterns(light)
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for x := 0; x < loResWidth; x++ {
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for y := 0; y < height; y++ {
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offset := (x % 2) * 2 // 2 pixel offset for odd lores pixels, 0 for even pixels
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c := getLoResPixel(a, x, y, page)
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// Insert the 14 half pixels required
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for i := 0; i < loResPixelWidth*2; i++ {
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v := patterns[c][i+offset]
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// Repeat the same color for 4 lines
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for r := 0; r < loResPixelHeight; r++ {
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img.Set(x*loResPixelWidth*2+i, y*4+r, v)
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}
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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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