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Prevent animation decoding from running into cel data

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This commit is contained in:
Jeremy Penner 2023-12-23 12:28:00 -05:00
parent eb758b7f3a
commit 79f14b8d39
1 changed files with 19 additions and 13 deletions
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30
index.js
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@ -228,7 +228,7 @@ const decodeWalkto = (byte) => {
}
const decodeProp = (data) => {
let prop = {
const prop = {
data: data,
howHeld: decodeHowHeld(data.getUint8(0)),
colorBitmask: data.getUint8(1),
@ -257,14 +257,26 @@ const decodeProp = (data) => {
allCelsMask != 0xf8 && allCelsMask != 0xfc && allCelsMask != 0xfe && allCelsMask != 0xff) {
throw new Error("Inconsistent graphic state cel masks - implies unused cel data")
}
let firstCelOff = Number.POSITIVE_INFINITY
for (let celOffsetOff = celOffsetsOff; allCelsMask != 0; celOffsetOff += 2) {
const icel = prop.cels.length
const celbit = 0x80 >> icel
const celOff = data.getUint16(celOffsetOff, LE)
firstCelOff = Math.min(celOff, firstCelOff)
prop.cels.push(decodeCel(new DataView(data.buffer, celOff), (prop.colorBitmask & celbit) != 0))
allCelsMask = (allCelsMask << 1) & 0xff
}
// The prop structure also does not encode a count for how many frames there are, so we simply
// stop parsing once we find one that doesn't make sense.
// We could also potentially assume that this structure always follows the header (or the
// "container" XY array, if one exists), as that seems to be consistently be the case with all
// the props in the Habitat source tree.
// We also use the heuristic that this structure always precedes the first cel, as that seems to be
// consistently be the case with all the props in the Habitat source tree. We'll stop reading
// animation data if we cross that boundary. If we encounter a prop that has the animation data
// _after_ the cel data, which would be legal but doesn't happen in practice, then we ignore this
// heuristic rather than failing to parse any animation data.
// It's possible for there to be no frames, which is represented by an offset of 0 (no_animation)
if (graphicStateOff != 0) {
for (let frameOff = graphicStateOff; ; frameOff += 2) {
for (let frameOff = graphicStateOff; (graphicStateOff > firstCelOff) || (frameOff < firstCelOff); frameOff += 2) {
// each animation is two bytes: the starting state, and the ending state
// the first byte can have its high bit set to indicate that the animation should cycle
const cycle = (data.getUint8(frameOff) & 0x80) != 0
@ -276,12 +288,6 @@ const decodeProp = (data) => {
prop.animations.push({ cycle: cycle, startState: startState, endState: endState })
}
}
for (let celOffsetOff = celOffsetsOff; allCelsMask != 0; celOffsetOff += 2) {
const icel = prop.cels.length
const celbit = 0x80 >> icel
prop.cels.push(decodeCel(new DataView(data.buffer, data.getUint16(celOffsetOff, LE)), (prop.colorBitmask & celbit) != 0))
allCelsMask = (allCelsMask << 1) & 0xff
}
return prop
}
@ -394,7 +400,7 @@ const displayList = async (indexFile, containerId) => {
const response = await fetch(indexFile)
const filenames = await response.json()
const container = document.getElementById(containerId)
for (filename of filenames) {
for (const filename of filenames) {
displayFile(filename, container)
}
}