izapple2/screenLoRes.go

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