izapple2/screen/loRes.go
2020-10-17 13:31:42 +02:00

94 lines
2.3 KiB
Go

package screen
import (
"image"
"image/color"
)
const (
loResPixelWidth = charWidth * 2
doubleLoResPixelWidth = charWidth
loResPixelHeight = charHeight / 2
)
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 snapshotLoRes(vs VideoSource, isSecondPage bool, light color.Color) *image.RGBA {
data := getTextFromMemory(vs, isSecondPage, false)
return renderGr(data, false /*isMeres*/, light)
}
func snapshotMeRes(vs VideoSource, isSecondPage bool, light color.Color) *image.RGBA {
data := getText80FromMemory(vs, isSecondPage)
return renderGr(data, true /*isMeres*/, light)
}
func renderGr(data []uint8, isDoubleResMode bool, light color.Color) *image.RGBA {
grLines := textLines * 2
columns := len(data) / textLines
pixelWidth := loResPixelWidth
if isDoubleResMode {
pixelWidth = doubleLoResPixelWidth
}
size := image.Rect(0, 0, columns*pixelWidth, grLines*loResPixelHeight)
img := image.NewRGBA(size)
patterns := getColorPatterns(light)
for l := 0; l < grLines; l++ {
for c := 0; c < columns; c++ {
char := data[(l/2)*columns+c]
grPixel := char >> 4
if l%2 == 0 {
grPixel = char & 0xf
}
// We place pixelWidth mono pixels per graphic pixel.
// The groups of 4 mono pixels need to be aligned with an offset to get plain surfaces
offset := (c * pixelWidth) % 4
if isDoubleResMode && ((c % 2) == 0) {
// See "Understanding the Apple II", page 8-44
// Even blocks color are rotated left one bit
offset = offset + 3 // Equivalent to -1
}
// Insert the pixelWidth pixels required
for i := 0; i < pixelWidth; i++ {
v := patterns[grPixel][i+offset]
// Repeat the same color for 4 lines
for r := 0; r < loResPixelHeight; r++ {
img.Set(c*pixelWidth+i, l*4+r, v)
}
}
}
}
return img
}