[Vm-dev] primitiveDisplayString fails on empty Strings

[Fabio Niephaus]

Hi Eliot,


On Wed, May 23, 2018 at 9:48 PM Eliot Miranda <eliot.miranda at gmail.com>
wrote:

>
> Hi Fabio,
>
>
>
> On Wed, May 23, 2018 at 12:11 PM, Fabio Niephaus <lists at fniephaus.com>
> wrote:
>
>>
>> Hi all,
>>
>> I noticed that BitBlt's primitiveDisplayString fails relatively often and
>> then found out that it's sometimes called to draw empty strings.
>>
>> `(ByteString allInstances select: [:ea | ea isEmpty]) size` revealed that
>> there are 2245 empty strings in my image and I assume some of them must be
>> either in the FrameRateMorph morph or in the Clock morph.
>>
>> Anyway...looking at BitBlt>>#primDisplayString:from:to:map:xTable:kern:,
>> the fallback code basically does nothing if stopIndex is zero (`startIndex
>> to: stopIndex do: ...`) which makes sense.
>>
>> What I think doesn't make sense is that the primitive fails in the first
>> place. Instead of failing if stopIndex is not greater 0, I would suggest to
>> use: `stopIndex < 1 ifTrue: [^ interpreterProxy pop: 6].` which cleans up
>> the stack, leaves the receiver, and returns early.
>>
>> Let me know what you think!
>>
>
> I don't object.  So you suggest the following?
>
> ((interpreterProxy isArray: xTable)
> and: [(interpreterProxy isArray: glyphMap)
> and: [(interpreterProxy slotSizeOf: glyphMap) = 256
> and: [(interpreterProxy isBytes: sourceString)
> and: [startIndex > 0
> and: [stopIndex > 0
> and: [stopIndex <= (interpreterProxy byteSizeOf: sourceString)
> and: [(self loadBitBltFrom: bbObj)
> and: [combinationRule ~= 30 "these two need extra source alpha"
> and: [combinationRule ~= 31]]]]]]]]]) ifFalse:
> [^interpreterProxy primitiveFail].
>
> =>
>
> ((interpreterProxy isArray: xTable)
> and: [(interpreterProxy isArray: glyphMap)
> and: [(interpreterProxy slotSizeOf: glyphMap) = 256
> and: [(interpreterProxy isBytes: sourceString)
> and: [startIndex > 0
> *and: [stopIndex >= 0 "to avoid failing for empty strings..."*
> and: [stopIndex <= (interpreterProxy byteSizeOf: sourceString)
> and: [(self loadBitBltFrom: bbObj)
> and: [combinationRule ~= 30 "these two need extra source alpha"
> and: [combinationRule ~= 31]]]]]]]]]) ifFalse:
> [^interpreterProxy primitiveFail].
>
> stopIndex = 0 ifTrue:
> [^interpreterProxy pop: 6. "the string is empty; pop args, return rcvr"].
>

> Any other opinions either way?
>

Why not do the stopIndex = 0 check early and move it all the way up? The
primitive won't fail if any of the other checks fail which I don't think is
bad if you don't want to draw anything (stopIndex = 0). On the other hand,
these other checks are not executed at all (e.g. loadBitBltFrom:) and you
don't have to change the stopIndex > 0 check. :)

Fabio


>
> _,,,^..^,,,_
> best, Eliot
>
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