grdimage: Fix uninitialized inc[] read with variable transparency - #9185
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For an image with variable transparency, GMT_grdimage does "goto tr_image", which jumps into the middle of the "if (need_to_project)" block and therefore skips the initializers of the variables declared there. nx_proj/ny_proj are reassigned before use, but inc[] is not, so gmt_project_init() branched on leftover stack bytes: when those happened to look like two positive doubles it derived the projected dimensions from inc[] instead of nx_proj/ny_proj and collapsed the image to 1x1 pixels, drawing a blank or degenerate panel. Since the outcome depended on stack contents, it failed on roughly half the runs, which is what made test/grdimage/image_vartrans.sh flaky. It affects any RGBA image with a variable alpha channel, with or without -Q. Declaring the variables at function scope keeps their initializers on every path into the block. Found with valgrind, which reports the read on every run - only its consequence is random. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Esteban82
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I simplified the comment. |
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test/grdimage/image_vartrans.shhas been failing intermittently, on roughly half the runs. I have seen this myself running the same script on different occasions: sometimes panels 3 and 4 come out fine, and sometimes they are blank.According to Claude the cause is an uninitialized variable. For images with a variable alpha channel,
GMT_grdimagedoesgoto tr_image, which jumps into theif (need_to_project)block past the declaration ofdouble inc[2] = {0.0, 0.0}, so the initializer never runs.gmt_project_init()then branches on that leftover stack value and, when it happens to look positive, projects the image to 1x1 pixels — a blank panel, with no warning. Hence the coin-flip behavior.This PR adds the fix proposed by Claude Opus 5.