Added variable threshold to makemask

Gadgetoid · May 20, 2021 · faf03e7 · faf03e7
1 parent fef4684
commit faf03e7
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Showing 3 changed files with 8 additions and 9 deletions.
diff --git a/src/PNGdec.cpp b/src/PNGdec.cpp
@@ -24,7 +24,7 @@
 // forward references
 PNG_STATIC int PNGInit(PNGIMAGE *pPNG);
 PNG_STATIC int DecodePNG(PNGIMAGE *pImage, void *pUser, int iOptions);
-PNG_STATIC void PNGMakeMask(PNGDRAW *pDraw, uint8_t *pMask);
+PNG_STATIC void PNGMakeMask(PNGDRAW *pDraw, uint8_t *pMask, uint8_t ucThreshold);
 // Include the C code which does the actual work
 #include "png.inl"
 
@@ -203,7 +203,7 @@ void PNG::getLineAsRGB565(PNGDRAW *pDraw, uint16_t *pPixels, int iEndianness, ui
     PNGRGB565(pDraw, pPixels, iEndianness, u32Bkgd, hasAlpha());
 } /* getLineAsRGB565() */
 
-void PNG::getAlphaMask(PNGDRAW *pDraw, uint8_t *pMask)
+void PNG::getAlphaMask(PNGDRAW *pDraw, uint8_t *pMask, uint8_t ucThreshold)
 {
-    PNGMakeMask(pDraw, pMask);
+    PNGMakeMask(pDraw, pMask, ucThreshold);
 } /* getAlphaMask() */
diff --git a/src/PNGdec.h b/src/PNGdec.h
@@ -181,7 +181,7 @@ class PNG
     int getBufferSize();
     uint8_t *getBuffer();
     void setBuffer(uint8_t *pBuffer);
-    void getAlphaMask(PNGDRAW *pDraw, uint8_t *pMask);
+    void getAlphaMask(PNGDRAW *pDraw, uint8_t *pMask, uint8_t ucThreshold);
     void getLineAsRGB565(PNGDRAW *pDraw, uint16_t *pPixels, int iEndianness, uint32_t u32Bkgd);
 
   private:

diff --git a/src/png.inl b/src/png.inl
@@ -93,11 +93,10 @@ uint8_t * PNG_getBuffer(PNGIMAGE *pPNG)
 } /* PNG_getBuffer() */
 
 #endif // !__cplusplus
-PNG_STATIC void PNGMakeMask(PNGDRAW *pDraw, uint8_t *pMask)
+PNG_STATIC void PNGMakeMask(PNGDRAW *pDraw, uint8_t *pMask, uint8_t ucThreshold)
 {
     uint8_t alpha, c, *s, *d, *pPal;
     int i, x;
-    const uint8_t ALPHA_THRESHOLD = 127;
 
     switch (pDraw->iPixelType) {
         case PNG_PIXEL_TRUECOLOR_ALPHA: // truecolor + alpha
@@ -108,7 +107,7 @@ PNG_STATIC void PNGMakeMask(PNGDRAW *pDraw, uint8_t *pMask)
                 for (i=0; i<8; i++) {
                     c <<= 1;
                     alpha = s[3];
-                   if (alpha > ALPHA_THRESHOLD) // if opaque 'enough', set the bit
+                   if (alpha >= ucThreshold) // if opaque 'enough', set the bit
                        c |= 1;
                     s += 4;
                 }
@@ -123,7 +122,7 @@ PNG_STATIC void PNGMakeMask(PNGDRAW *pDraw, uint8_t *pMask)
                 for (i=0; i<8; i++) {
                     c <<= 1;
                     alpha = s[1];
-                   if (alpha > ALPHA_THRESHOLD) // if opaque 'enough', set the bit
+                   if (alpha >= ucThreshold) // if opaque 'enough', set the bit
                        c |= 1;
                     s += 2;
                 }
@@ -139,7 +138,7 @@ PNG_STATIC void PNGMakeMask(PNGDRAW *pDraw, uint8_t *pMask)
                 for (i=0; i<8; i++) {
                     c <<= 1;
                     alpha = pPal[s[0]]; // get palette alpha for this color
-                   if (alpha > ALPHA_THRESHOLD) // if opaque 'enough', set the bit
+                   if (alpha >= ucThreshold) // if opaque 'enough', set the bit
                        c |= 1;
                     s++;
                 }