perf: improve dashboard graph Y domain heuristic
Change-Id: I15e3f03c75907cc257040799cbd7f4df8b790a69
Reviewed-on: https://go-review.googlesource.com/c/build/+/412380
Reviewed-by: Michael Pratt <mpratt@google.com>
diff --git a/third_party/bandchart/bandchart.js b/third_party/bandchart/bandchart.js
index 9e2ba69..f9b0f2f 100644
--- a/third_party/bandchart/bandchart.js
+++ b/third_party/bandchart/bandchart.js
@@ -27,13 +27,46 @@
// Compute default domains.
let yDomain = d3.nice(...d3.extent([...Y1, ...Y2]), 10);
- // Don't show <2.5% up-close because it just looks extremely noisy.
+
+ // Determine Y domain.
+ //
+ // Three cases:
+ // (1) All data is above Y=0 line.
+ // (2) All data is below Y=0 line.
+ // (3) Data crosses the Y=0 line.
+ //
+ // For (1) set the Y=0 line as the bottom of the domain.
+ // For (2) set it at the top.
+ // For (3) make sure the Y=0 line is in the middle.
+ //
+ // Finally, make sure we don't get closer than 0.025,
+ // bceuase otherwise it just looks really noisy.
const minYDomain = [-0.025, 0.025];
- if (yDomain[0] > minYDomain[0]) {
- yDomain[0] = minYDomain[0];
- }
- if (yDomain[1] < minYDomain[1]) {
- yDomain[1] = minYDomain[1];
+ if (yDomain[0] > 0) {
+ // (1)
+ yDomain[0] = 0;
+ if (yDomain[1] < minYDomain[1]) {
+ yDomain[1] = minYDomain[1];
+ }
+ } else if (yDomain[1] < 0) {
+ // (2)
+ yDomain[1] = 0;
+ if (yDomain[0] > minYDomain[0]) {
+ yDomain[0] = minYDomain[0];
+ }
+ } else {
+ // (3)
+ if (Math.abs(yDomain[1]) > Math.abs(yDomain[0])) {
+ yDomain[0] = -Math.abs(yDomain[1]);
+ } else {
+ yDomain[1] = Math.abs(yDomain[0]);
+ }
+ if (yDomain[0] > minYDomain[0]) {
+ yDomain[0] = minYDomain[0];
+ }
+ if (yDomain[1] < minYDomain[1]) {
+ yDomain[1] = minYDomain[1];
+ }
}
// Construct scales and axes.
