diff --git a/Display.md b/Display.md
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@@ -7,4 +7,8 @@ Right now, we're drawing all the spheres in a single fragment shader. For each p
 ## Performance limits
 
 * **Array size.** As of commit `a34fd0f`, the SPHERE_MAX array size seems to affect frame rate a lot, even though we should only be using the first few elements of each array. Not sure whether this is coming from a depth-sorting bug, a memory handling detail, or something else.
-* **Shader variables.** Browsers seem to limit the number of variables that fragment shaders can store. For example, see this [vulnerability report](https://issues.chromium.org/issues/40067239) and [code review](https://chromium-review.googlesource.com/c/angle/angle/+/4503753) for Chromium. This limit doesn't seem to be part of the OpenGL standard, so it's hard to pin down.
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+* **Shader variables.** Browsers seem to limit the number of variables that fragment shaders can store. For example, see this [vulnerability report](https://issues.chromium.org/issues/40067239) and [code review](https://chromium-review.googlesource.com/c/angle/angle/+/4503753) for Chromium. This limit doesn't seem to be part of the OpenGL standard, so it's hard to pin down.
+
+## References
+
+[This tutorial](https://jamie-wong.com/2016/07/06/metaballs-and-webgl) on metaballs describes various ways to pass object data into a fragment shader that draws many objects.
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