David T. Lewis uploaded a new version of VMMaker to project VM Maker: http://source.squeak.org/VMMaker/VMMaker.oscog-dtl.568.mcz
==================== Summary ====================
Name: VMMaker.oscog-dtl.568 Author: dtl Time: 21 December 2013, 11:50:53.68 am UUID: 527f0c71-198d-4adf-804c-53c6842e9124 Ancestors: VMMaker.oscog-eem.567
Check for valid bitmap in primitivePixelValueAt aka BitBltSimulation>>primitivePixelValueAtX:y: Fix provided by Nicolas Cellier Reference Mantis 7799
=============== Diff against VMMaker.oscog-eem.567 ===============
Item was changed: ----- Method: BitBltSimulation>>primitivePixelValueAtX:y: (in category 'primitives') ----- primitivePixelValueAtX: xVal y: yVal "returns the single pixel at x@y. It does not handle LSB bitmaps right now. If x or y are < 0, return 0 to indicate transparent (cf BitBlt>bitPeekerFromForm: usage). Likewise if x>width or y>depth. Fail if the rcvr doesn't seem to be a Form, or x|y seem wrong" + | rcvr bitmap depth ppW stride bitsSize word mask shift pixel | - | rcvr bitmap depth ppW stride word mask shift pixel | rcvr := self primitive: 'primitivePixelValueAt' parameters: #(SmallInteger SmallInteger) receiver: #Oop. "possible quick exit if x or y is -ve" (xVal < 0 or: [ yVal < 0 ] ) ifTrue:[^interpreterProxy integerObjectOf: 0]. "check that rcvr is plausibly a Form or subclass" rcvr := interpreterProxy stackValue: interpreterProxy methodArgumentCount. ((interpreterProxy isPointers: rcvr) and: [(interpreterProxy slotSizeOf: rcvr) >= 4]) ifFalse: [^interpreterProxy primitiveFail].
"get the bits oop and width/height/depth" bitmap := interpreterProxy fetchPointer: FormBitsIndex ofObject: rcvr. + (interpreterProxy isWordsOrBytes: bitmap) ifFalse: [^interpreterProxy primitiveFail]. width := interpreterProxy fetchInteger: FormWidthIndex ofObject: rcvr. height := interpreterProxy fetchInteger: FormHeightIndex ofObject: rcvr. depth := interpreterProxy fetchInteger: FormDepthIndex ofObject: rcvr. "if width/height/depth are not integer, fail" interpreterProxy failed ifTrue:[^nil].
"possible quick exit if x or y is >= extent of form. This also catches cases where the width/height are < 0" (xVal >= width or: [ yVal >= height ] ) ifTrue:[^interpreterProxy integerObjectOf: 0].
"we don't handle LSB Forms yet" depth < 0 ifTrue:[^interpreterProxy primitiveFail]. "OK so now we know we have a plausible Form, the width/height/depth/x/y are all reasonable and it's time to plunder the bitmap" ppW := 32//depth. "pixels in each word" + stride := (width + (ppW -1)) // ppW. "how many words per row of pixels" + bitsSize := interpreterProxy byteSizeOf: bitmap. + bitsSize = (stride * height * 4 "bytes per word") + ifFalse: [^interpreterProxy primitiveFail]. - stride := (width + (ppW -1)) // ppW. "how many words per rox of pixels" word := interpreterProxy fetchLong32:(yVal * stride) + (xVal//ppW) ofObject: bitmap. "load the word that contains our target" mask := 16rFFFFFFFF >> (32 - depth). "make a mask to isolate the pixel within that word" shift := 32 - (((xVal bitAnd: ppW-1) + 1) * depth). "this is the tricky MSB part - we mask the xVal to find how far into the word we need, then add 1 for the pixel we're looking for, then * depth to get the bit shift" pixel := (word >> shift) bitAnd: mask. "shift, mask and dim the lights" ^ pixel asPositiveIntegerObj "pop the incoming and push our answer" !