132 lines
2.7 KiB
Go
132 lines
2.7 KiB
Go
// Copyright 2021-2024 Sebastian Lederer. See the file LICENSE.md for details
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package main
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import (
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// "fmt"
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"image/color"
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"github.com/hajimehoshi/ebiten/v2"
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)
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const VmemWords = 32768
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const PaletteSlots = 16
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const FB_RA = 0
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const FB_WA = 1
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const FB_IO = 2
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const FB_PS = 3
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const FB_PD = 4
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const FB_CTL= 5
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const PixelMask = 0b11110000000000000000000000000000
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const PixelPerWord = 8
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const VmemWidth = 32
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const BitsPerPixel = 4
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const ScreenWidth = 640
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const ScreenHeight = 400
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const WordsPerLine = ScreenWidth / PixelPerWord
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type Framebuffer struct {
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framebuffer *ebiten.Image
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palette [PaletteSlots] color.Color
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readAddr word
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writeAddr word
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paletteSlot word
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vmem [VmemWords]word
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readCount int
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}
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func (f *Framebuffer) initialize() {
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f.framebuffer = ebiten.NewImage(ScreenWidth, ScreenHeight)
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for i := 0; i <PaletteSlots; i++ {
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f.palette[i] = color.RGBA{0,0,0,0}
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}
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}
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func (f *Framebuffer) read(byteaddr word) (word, error) {
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result := word(0)
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addr := byteaddr & 0x7F
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switch addr {
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case FB_RA: result = f.readAddr
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case FB_WA: result = f.writeAddr
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case FB_IO: result = f.readVmem()
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case FB_PS: result = f.paletteSlot
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case FB_PD: result = f.readPalette()
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case FB_CTL: result = f.readCtl()
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default:
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}
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return result, nil
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}
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func (f *Framebuffer) write(value word, byteaddr word) (error) {
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addr := byteaddr & 0x7F
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switch addr {
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case FB_RA: f.readAddr = value
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case FB_WA: f.writeAddr = value
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case FB_IO: f.writeVmem(value)
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case FB_PS: f.paletteSlot = value
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case FB_PD: f.writePalette(value)
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case FB_CTL: f.writeCtl(value)
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default:
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}
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idle(false)
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return nil
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}
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func (f *Framebuffer) readVmem() word {
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result := f.vmem[f.readAddr & (VmemWords - 1)]
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f.readAddr += 1
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return result
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}
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func (f *Framebuffer) writeVmem(value word) {
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vaddr := f.writeAddr & (VmemWords - 1)
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f.vmem[vaddr] = value
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y := vaddr / WordsPerLine
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x := vaddr % WordsPerLine * PixelPerWord
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for i := 0; i < PixelPerWord; i++ {
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pixel := (value & PixelMask) >> (VmemWidth - BitsPerPixel)
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value = value << BitsPerPixel
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col := f.palette[pixel]
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//fmt.Printf("set pixel %v, %v\n", x,y)
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f.framebuffer.Set(int(x), int(y), col)
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x = x + 1
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}
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f.writeAddr += 1
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}
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func (f *Framebuffer) readPalette() word {
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return word(0)
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}
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func (f *Framebuffer) writePalette(value word) {
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// 4 bits per color channel
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r := uint8((value & 0b111100000000) >> 8)
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g := uint8((value & 0b000011110000) >> 4)
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b := uint8((value & 0b000000001111) >> 0)
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// scale to 0-255
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r = r << 4
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g = g << 4
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b = b << 4
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f.palette[f.paletteSlot] = color.RGBA{r,g,b,0}
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}
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func (f *Framebuffer) readCtl() word {
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if f.readCount == 0 {
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f.readCount = 1000
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return word(0)
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} else {
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f.readCount -= 1
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return word(1)
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}
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}
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func (f *Framebuffer) writeCtl(value word) {
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}
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