glplanet, an OpenGL-based planetary rendererHEADmain

glplanet draws Earth like it currently appears from space, putting
nighttime areas in shadow and daytime areas in light. It’s modeled
after Xplanet (http://xplanet.sourceforge.net/), but whereas Xplanet is
entirely a CPU-resident program, glplanet draws using OpenGL. It’s thus
much less resource-intensive, particularly when using high-resolution
textures.

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+This directory defines an idiomatic C++ interface to parts of OpenGL.
+
+This library requires OpenGL 3.2 with the following extensions:
+  - ARB_texture_storage (or OpenGL >=4.2)
+  - ARB_direct_state_access (or OpenGL >=4.5)
+
+OpenGL is an inherently thread-hostile interface (it uses thread-local state).
+By default, this library will throw if it detects it is being used in a
+thread-unsafe way. However, this checking does carry a performance cost, so
+defining GLPLANET_DISABLE_GL_THREAD_SAFETY_CHECKS disables these checks.
+
+By default, this library throws OpenGL errors as soon as they occur. This makes
+debugging easier, since it associates errors more closely with the operations to
+which they correspond. However, this bookkeeping carries a performance cost;
+defining GLPLANET_DISABLE_AGGRESSIVE_ERROR_CHECKING will reduce it to the
+absolute minimum required for correctness.