debug.patch

diff --git a/setup.py b/setup.py
index 4163147..75f1989 100755
--- a/setup.py
+++ b/setup.py
@@ -297,6 +297,8 @@ class CustomBuildExt(build_ext):
                 e.extra_compile_args.append("-Wno-unused-function") # quell some annoying warnings
                 e.extra_compile_args.append("-Wdeclaration-after-statement")
                 e.extra_compile_args.append("-Werror=declaration-after-statement")
+                e.extra_compile_args.append("-g")
+                e.extra_compile_args.append("-O0")
 
 
         # build in place, and in the build/ tree

demo-config.py

worlds["Debug World"] = "/root/Overviewer-Test-Data-master/world_189"

renders["day"] = {
    "world": "Debug World",
    "title": "Daytime",
    "rendermode": smooth_lighting,
    "dimension": "overworld",
}

outputdir = "/tmp/overviewer-debug-output"

Dockerfile

FROM ubuntu:16.04

RUN apt-get -y update
RUN apt-get -y install gcc gdb curl wget git-core \
    python python-dev python-dbg \
    python-imaging python-imaging-dbg \
    python-numpy python-pip

WORKDIR /root

RUN pip install pillow==4.3.0

RUN git clone git://github.com/overviewer/Minecraft-Overviewer.git && \
    cd Minecraft-Overviewer && \
    curl -sL https://gist.github.com/aheadley/a95ff794bd98741c3f5dc6c5361b829a/raw/eef6ea57ad9e37d1f30684628361404184b0ba24/debug.patch | patch -p1 && \
    ./setup.py build

RUN curl -sL https://github.com/overviewer/Overviewer-Test-Data/archive/master.tar.gz | tar xzf - && \
    curl -sL https://gist.github.com/aheadley/a95ff794bd98741c3f5dc6c5361b829a/raw/eef6ea57ad9e37d1f30684628361404184b0ba24/demo-config.py > demo-config.py && \
    wget -q https://s3.amazonaws.com/Minecraft.Download/versions/1.12/1.12.jar -P ~/.minecraft/versions/1.12/