derive default line width from display dpi

allows better default on high dpi displays where the previous
default of 1 pixel would've been too small.

Closes: #285
Co-authored-by: Guilherme Janczak <guilherme.janczak@yandex.com>

Author: N-R-K

man/scrot.txt

@@ -175,7 +175,9 @@ SELECTION STYLE
 
   Without the -l option, a default style is used:
 
-    mode=auto,style=solid,width=1,opacity=100
+    mode=auto,style=solid,opacity=100
+
+  The default width is automatically derived from the display DPI.
 
   Example:
 

src/options.c

@@ -68,7 +68,6 @@ struct ScrotOptions opt = {
     .quality = 75,
     .compression = 7,
     .lineStyle = LineSolid,
-    .lineWidth = 1,
     .lineOpacity = SELECTION_OPACITY_DEFAULT,
     .stackDirection = HORIZONTAL,
     .outputFile = defaultOutputFile,

src/scrot_selection.c

@@ -423,6 +423,11 @@ Imlib_Image scrotSelectionSelectMode(void)
             opt.lineMode = LINE_MODE_CLASSIC;
     }
 
+    if (opt.lineWidth == 0) {
+        int width = (scr->height + scr->width) / (scr->mheight + scr->mwidth);
+        opt.lineWidth = MIN(MAX(width/4, 1), 8);
+    }
+
     if (opt.delaySelection)
         scrotDoDelay();
 

src/util.h

@@ -43,6 +43,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 #define ARRAY_COUNT(X)   (sizeof(X) / sizeof(0[X]))
 #define MAX(A, B)        ((A) > (B) ? (A) : (B))
+#define MIN(A, B)        ((A) < (B) ? (A) : (B))
 
 typedef struct {
     char *buf;