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A Qt/OpenGL-based implementation of a heap history visualisation UI in along the lines of Gerardo Richarte's HeapDraw (for more details, check

The tool had been reimplemented by various people in various places a few times, usually in a hackish / nonscalable manner. zynamics used to hand source code for a JOGL-based UI out with some of our trainings, but that tool is not easily portable to modern OpenGL or 64-bit address spaces.

Other common mistakes include:

  • Not using OpenGL to render lots of rectangles.
  • Using floats or other low-precision coordinates to represent rectangle corners and hence suffering from rounding errors.
  • Not using a language that can deal with a couple million rectangles.

The codebase in this repository has the following goals:

  • Fast and scalable to 20m+ allocations. Haven't tried, but should work.
  • As precise as possible. Use precise integer arithmetic as much as possible to avoid rounding errors shifting rectangles around.
  • Useable. This will take some time.

Instructions for the moment:

  • Build using stock QtCreator.
  • You will need: libgflags-dev mesa-common-dev libqt4-opengl-dev
  • The current trunk will simply try to load /tmp/heap.json - use the enclosed json file as an example.

A million tasks are still left to do. Useful things that should be added:

  • Code to display tooltips when the mouse hovers over a block.
  • Code to highlight a block when it is clicked / selected.
  • Code to add horizontal red lines, too.
  • Code to select all blocks that are modified between two events.
  • ...

Contributions very welcome.

Basic controls:

  • CTRL + wheel: Zoom in / out
  • Click + drag: Pan diagram
  • CTRL + shift + wheel: Squash / stretch horizontally
  • shift + wheel: Squash / stretch vertically

Cheers, Halvar Flake / Thomas Dullien


A program to draw rectangles from heap traces.







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