martino/plotter
1
0 Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

fix(math): keep from_range invertible for collapsed pixel spans

Browse Source 
A zero pixel span previously produced sx/sy == 0, so to_data_* returned
NaN or +/-inf. axis_scale now substitutes a unit pixel span (1.0) when
|p1 - p0| <= 1e-12, keeping the mapping finite and invertible while
leaving non-collapsed spans byte-identical.

Add committed coverage for from_range (linear, flipped pixel axis, log x,
degenerate data range, collapsed pixel span) and log10_positive clamping.
This commit is contained in:
Martino Ferrari committed 2026-09-27 20:58:37 +02:00
1 parent 8a7e9e97f8
commit ed71719df7
2 files changed
+84 -2
Download Patch File Download Diff File Expand all files Collapse all files

No files matched your search

tests/test_transform.cpp
+62
View File
@@ -29,3 +29,65 @@ PLOT_TEST(zoom_anchor_is_invariant) {
t.tx = before - anchor_data * t.sx;
PLOT_CHECK_NEAR(t.to_screen_x(anchor_data), before, 1e-12);
}
PLOT_TEST(from_range_linear) {
const Transform t =
Transform::from_range({0.0, 10.0}, {-1.0, 1.0}, 0.0, 100.0, 0.0, 200.0, false, false);
PLOT_CHECK_NEAR(t.to_screen_x(0.0), 0.0, 1e-12);
PLOT_CHECK_NEAR(t.to_screen_x(10.0), 100.0, 1e-12);
PLOT_CHECK_NEAR(t.to_screen_y(-1.0), 0.0, 1e-12);
PLOT_CHECK_NEAR(t.to_screen_y(1.0), 200.0, 1e-12);
PLOT_CHECK_NEAR(t.to_data_x(t.to_screen_x(3.5)), 3.5, 1e-12);
PLOT_CHECK_NEAR(t.to_data_y(t.to_screen_y(0.25)), 0.25, 1e-12);
}
PLOT_TEST(from_range_flipped_pixel_axis) {
// px0 > px1 reverses the direction of the axis; the round trip must survive.
const Transform t =
Transform::from_range({0.0, 10.0}, {0.0, 10.0}, 100.0, 0.0, 200.0, 0.0, false, false);
PLOT_CHECK_NEAR(t.to_screen_x(0.0), 100.0, 1e-12);
PLOT_CHECK_NEAR(t.to_screen_x(10.0), 0.0, 1e-12);
PLOT_CHECK_NEAR(t.to_screen_y(0.0), 200.0, 1e-12);
PLOT_CHECK_NEAR(t.to_screen_y(10.0), 0.0, 1e-12);
PLOT_CHECK_NEAR(t.to_data_x(t.to_screen_x(2.5)), 2.5, 1e-12);
PLOT_CHECK_NEAR(t.to_data_y(t.to_screen_y(7.5)), 7.5, 1e-12);
}
PLOT_TEST(from_range_log_x) {
const Transform t =
Transform::from_range({1.0, 1000.0}, {0.0, 1.0}, 0.0, 300.0, 0.0, 100.0, true, false);
PLOT_CHECK(t.log_x);
PLOT_CHECK(!t.log_y);
PLOT_CHECK_NEAR(t.to_screen_x(1.0), 0.0, 1e-12);
PLOT_CHECK_NEAR(t.to_screen_x(1000.0), 300.0, 1e-12);
// log10(31.6227766) == 1.5 lands exactly halfway along the axis.
PLOT_CHECK_NEAR(t.to_screen_x(31.6227766), 150.0, 1e-6);
PLOT_CHECK_NEAR(t.to_data_x(t.to_screen_x(31.6227766)), 31.6227766, 1e-9);
}
PLOT_TEST(from_range_degenerate_data_range) {
// min == max: the range is widened, so the mapping stays finite and invertible.
const Transform t =
Transform::from_range({5.0, 5.0}, {2.0, 2.0}, 0.0, 100.0, 0.0, 200.0, false, false);
PLOT_CHECK(std::isfinite(t.sx) && t.sx != 0.0);
PLOT_CHECK(std::isfinite(t.sy) && t.sy != 0.0);
PLOT_CHECK_NEAR(t.to_data_x(t.to_screen_x(5.0)), 5.0, 1e-9);
PLOT_CHECK_NEAR(t.to_data_y(t.to_screen_y(2.0)), 2.0, 1e-9);
}
PLOT_TEST(from_range_collapsed_pixel_span) {
// px0 == px1 previously gave sx == 0, so to_data_x returned NaN/inf.
const Transform t =
Transform::from_range({0.0, 10.0}, {0.0, 10.0}, 50.0, 50.0, 25.0, 25.0, false, false);
PLOT_CHECK(std::isfinite(t.sx) && t.sx != 0.0);
PLOT_CHECK(std::isfinite(t.sy) && t.sy != 0.0);
PLOT_CHECK_NEAR(t.to_data_x(t.to_screen_x(4.0)), 4.0, 1e-9);
PLOT_CHECK_NEAR(t.to_data_y(t.to_screen_y(7.0)), 7.0, 1e-9);
PLOT_CHECK(std::isfinite(t.to_data_x(t.to_screen_x(0.0))));
PLOT_CHECK(std::isfinite(t.to_data_y(t.to_screen_y(10.0))));
}
PLOT_TEST(log10_positive_clamps_non_positive) {
PLOT_CHECK(std::isfinite(Transform::log10_positive(0.0)));
PLOT_CHECK(std::isfinite(Transform::log10_positive(-5.0)));
PLOT_CHECK_NEAR(Transform::log10_positive(1.0), 0.0, 1e-12);
}