emscripten-core/emscripten

glMapBufferData requires INVALIDATE_BUFFER?

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#6,692 opened on Jun 13, 2018

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GLgood first bughelp wanted

Description

The emulation for glMapBufferRange requires MAP_WRITE and INVALIDATE_BUFFER here: https://github.com/kripken/emscripten/blob/a4d732f3094cfb2377609e1661044679f9c79734/src/library_gl.js#L1744

Under the hood, in glUnmapBufferData, the call is translated into a glBufferSubData. I don't think requiring INVALIDATE_BUFFER is correct here -- that means that the entire buffer should be discarded, not just the range that's mapped (which is INVALIDATE_RANGE). I think that:

  1. The requirement should be changed to INVALIDATE_RANGE
  2. A check should be done that there isn't an existing mapping for that buffer (additional restriction of only one range mapping per buffer, which GL doesn't have -- this could be relaxed with additional code, but probably not necessary in practice)

(Note I haven't tested any of this, this is just by code inspection from a question someone asked)

Contributor guide

Tech stack
javascriptcppwasm
Domain
api
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
basic knowledge of WebGLunderstanding of emscripten's GL emulation
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
The issue points to a specific function in `library gl.js` (line 1744). The fix involves changing the bit check from `INVALIDATE BUFFER` to `INVALIDATE RANGE` and adding a check for existing mappings. The issue has 2 comments that may provide additional context. Reproduce the bug by mapping a buffer without `INVALIDATE BUFFER` flag and observe the error, then implement the suggested changes and test with WebGL conformance suite.
glMapBufferData requires INVALIDATE_BUFFER? · emscripten-core/emscripten#6692 | Good First Issue