Backport PR #12117: Fix Agg extent calculations for empty draws

NelleV · dstansby · commit bfa8b8879f52 · 2018-09-16T10:29:41.000+01:00
diff --git a/lib/matplotlib/tests/test_backend_pdf.py b/lib/matplotlib/tests/test_backend_pdf.py
@@ -238,3 +238,11 @@ def test_failing_latex(tmpdir):
     plt.xlabel("$22_2_2$")
     with pytest.raises(RuntimeError):
         plt.savefig(path)
+
+
+def test_empty_rasterised():
+    # Check that emtpy figures that are rasterised save to pdf files fine
+    with PdfPages(io.BytesIO()) as pdf:
+        fig, ax = plt.subplots()
+        ax.plot([], [], rasterized=True)
+        fig.savefig(pdf, format="pdf")
diff --git a/src/_backend_agg.cpp b/src/_backend_agg.cpp
@@ -213,10 +213,15 @@ agg::rect_i RendererAgg::get_content_extents()
         }
     }
 
-    r.x1 = std::max(0, r.x1);
-    r.y1 = std::max(0, r.y1);
-    r.x2 = std::min(r.x2 + 1, (int)width);
-    r.y2 = std::min(r.y2 + 1, (int)height);
+    if (r.x1 == width && r.x2 == 0) {
+      // The buffer is completely empty.
+      r.x1 = r.y1 = r.x2 = r.y2 = 0;
+    } else {
+      r.x1 = std::max(0, r.x1);
+      r.y1 = std::max(0, r.y1);
+      r.x2 = std::min(r.x2 + 1, (int)width);
+      r.y2 = std::min(r.y2 + 1, (int)height);
+    }
 
     return r;
 }

Original file line number	Diff line number	Diff line change
`@@ -213,10 +213,15 @@ agg::rect_i RendererAgg::get_content_extents()`
`213`	`213`	`}`
`214`	`214`	`}`
`215`	`215`
`216`		`- r.x1 = std::max(0, r.x1);`
`217`		`- r.y1 = std::max(0, r.y1);`
`218`		`- r.x2 = std::min(r.x2 + 1, (int)width);`
`219`		`- r.y2 = std::min(r.y2 + 1, (int)height);`
	`216`	`+ if (r.x1 == width && r.x2 == 0) {`
	`217`	`+ // The buffer is completely empty.`
	`218`	`+ r.x1 = r.y1 = r.x2 = r.y2 = 0;`
	`219`	`+ } else {`
	`220`	`+ r.x1 = std::max(0, r.x1);`
	`221`	`+ r.y1 = std::max(0, r.y1);`
	`222`	`+ r.x2 = std::min(r.x2 + 1, (int)width);`
	`223`	`+ r.y2 = std::min(r.y2 + 1, (int)height);`
	`224`	`+ }`
`220`	`225`
`221`	`226`	`return r;`
`222`	`227`	`}`