initial commit

tridoraemu/framebuffer.go

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