pdftocairo: allow one of -scale-to-[xy] = -1 to mean the aspect ratio is to be preserved

based on pdftoppm patch 38ace7db5de0b2b247fd520e48a8f26e5d28c9d7

2 files changed, 12 insertions, 4 deletions

diff --git a/utils/pdftocairo.1 b/utils/pdftocairo.1
index 28e181f3..d02095ee 100644
--- a/utils/pdftocairo.1
+++ b/utils/pdftocairo.1
@@ -115,10 +115,14 @@ Specifies the Y resolution, in pixels per inch of image files (or rasterized reg
 Scales each page to fit in scale-to*scale-to pixel box (PNG/JPEG only).
 .TP
 .BI \-scale-to-x " number"
-Scales each page horizontally to fit in scale-to-x pixels (PNG/JPEG only).
+Scales each page horizontally to fit in scale-to-x pixels. If
+scale-to-y is set to -1, the vertical size will determined by the
+aspect ratio of the page (PNG/JPEG only).
 .TP
 .BI \-scale-to-y " number"
-Scales each page vertically to fit in scale-to-y pixels (PNG/JPEG only).
+Scales each page vertically to fit in scale-to-y pixels. If scale-to-x
+is set to -1, the horizontal size will determined by the aspect ratio
+of the page (PNG/JPEG only).
 .TP
 .BI \-x " number"
 Specifies the x-coordinate of the crop area top left corner in pixels (image output) or points (vector output)
diff --git a/utils/pdftocairo.cc b/utils/pdftocairo.cc
index 0d920ac3..2eeb7511 100644
--- a/utils/pdftocairo.cc
+++ b/utils/pdftocairo.cc
@@ -952,11 +952,15 @@ int main(int argc, char *argv[]) {
       resolution = (72.0 * scaleTo) / (pg_w > pg_h ? pg_w : pg_h);
       x_resolution = y_resolution = resolution;
     } else {
-      if (x_scaleTo != 0) {
+      if (x_scaleTo > 0) {
         x_resolution = (72.0 * x_scaleTo) / pg_w;
+        if (y_scaleTo == -1)
+          y_resolution = x_resolution;
       }
-      if (y_scaleTo != 0) {
+      if (y_scaleTo > 0) {
         y_resolution = (72.0 * y_scaleTo) / pg_h;
+        if (x_scaleTo == -1)
+          x_resolution = y_resolution;
       }
     }
     if ((doc->getPageRotate(pg) == 90) || (doc->getPageRotate(pg) == 270)) {