svg_loader: define the scaling factors for units changing

The values in absolute units are calculated based on the pixel unit.
Till now the default value of 90dpi was used. Since CSS3 (now CSS4 is
the most recent) 1 inch equals to 96 pixels. The necessary constants
are introduces in this commit.

diff --git a/src/loaders/svg/tvgSvgLoader.cpp b/src/loaders/svg/tvgSvgLoader.cpp
index 3ca7bdb..e587c3a 100644 (file)
--- a/src/loaders/svg/tvgSvgLoader.cpp
+++ b/src/loaders/svg/tvgSvgLoader.cpp
@@ -64,6 +64,17 @@
 /* Internal Class Implementation                                        */
 /************************************************************************/
 
+/*
+ * According to: https://www.w3.org/TR/SVG2/coords.html#Units
+ * and: https://www.w3.org/TR/css-values-4/#absolute-lengths
+ */
+#define PX_PER_IN 96        //1 in = 96 px
+#define PX_PER_PC 16        //1 pc = 1/6 in  -> PX_PER_IN/6
+#define PX_PER_PT 1.333333f //1 pt = 1/72 in -> PX_PER_IN/72
+#define PX_PER_MM 3.779528f //1 in = 25.4 mm -> PX_PER_IN/25.4
+#define PX_PER_CM 37.79528f //1 in = 2.54 cm -> PX_PER_IN/2.54
+
+
 typedef SvgNode* (*FactoryMethod)(SvgLoaderData* loader, SvgNode* parent, const char* buf, unsigned bufLength);
 typedef SvgStyleGradient* (*GradientFactoryMethod)(SvgLoaderData* loader, const char* buf, unsigned bufLength);
 
@@ -107,20 +118,16 @@ static bool _parseNumber(const char** content, float* number)
 
 /**
  * According to https://www.w3.org/TR/SVG/coords.html#Units
- *
- * TODO
- * Since this documentation is not obvious, more clean recalculation with dpi
- * is required, but for now default w3 constants would be used
  */
 static float _toFloat(const SvgParser* svgParse, const char* str, SvgParserLengthType type)
 {
     float parsedValue = svgUtilStrtof(str, nullptr);
 
-    if (strstr(str, "cm")) parsedValue = parsedValue * 35.43307;
-    else if (strstr(str, "mm")) parsedValue = parsedValue * 3.543307;
-    else if (strstr(str, "pt")) parsedValue = parsedValue * 1.25;
-    else if (strstr(str, "pc")) parsedValue = parsedValue * 15;
-    else if (strstr(str, "in")) parsedValue = parsedValue * 90;
+    if (strstr(str, "cm")) parsedValue *= PX_PER_CM;
+    else if (strstr(str, "mm")) parsedValue *= PX_PER_MM;
+    else if (strstr(str, "pt")) parsedValue *= PX_PER_PT;
+    else if (strstr(str, "pc")) parsedValue *= PX_PER_PC;
+    else if (strstr(str, "in")) parsedValue *= PX_PER_IN;
     else if (strstr(str, "%")) {
         if (type == SvgParserLengthType::Vertical) parsedValue = (parsedValue / 100.0) * svgParse->global.h;
         else if (type == SvgParserLengthType::Horizontal) parsedValue = (parsedValue / 100.0) * svgParse->global.w;
@@ -132,7 +139,6 @@ static float _toFloat(const SvgParser* svgParse, const char* str, SvgParserLengt
             parsedValue = (parsedValue / 100.0) * max;
         }
     }
-
     //TODO: Implement 'em', 'ex' attributes
 
     return parsedValue;
@@ -150,11 +156,11 @@ static float _gradientToFloat(const SvgParser* svgParse, const char* str, bool&
         parsedValue = parsedValue / 100.0;
         isPercentage = true;
     }
-    else if (strstr(str, "cm")) parsedValue = parsedValue * 35.43307;
-    else if (strstr(str, "mm")) parsedValue = parsedValue * 3.543307;
-    else if (strstr(str, "pt")) parsedValue = parsedValue * 1.25;
-    else if (strstr(str, "pc")) parsedValue = parsedValue * 15;
-    else if (strstr(str, "in")) parsedValue = parsedValue * 90;
+    else if (strstr(str, "cm")) parsedValue *= PX_PER_CM;
+    else if (strstr(str, "mm")) parsedValue *= PX_PER_MM;
+    else if (strstr(str, "pt")) parsedValue *= PX_PER_PT;
+    else if (strstr(str, "pc")) parsedValue *= PX_PER_PC;
+    else if (strstr(str, "in")) parsedValue *= PX_PER_IN;
     //TODO: Implement 'em', 'ex' attributes
 
     return parsedValue;