add lossless quick encoding functions to the public API

New functions:
   WebPEncodeLosslessRGB()
   WebPEncodeLosslessBGR()
   WebPEncodeLosslessRGBA()
   WebPEncodeLosslessBGRA()

Change-Id: Id56da7569eee80c57de8f1f053fb87b217d33a4b

README

@@ -263,6 +263,20 @@ size_t WebPEncodeBGRA(const uint8_t* bgra, int width, int height, int stride,
 They will convert raw RGB samples to a WebP data. The only control supplied
 is the quality factor.
 
+There are some variants for using the lossless format:
+
+size_t WebPEncodeLosslessRGB(const uint8_t* rgb, int width, int height,
+                             int stride, uint8_t** output);
+size_t WebPEncodeLosslessBGR(const uint8_t* bgr, int width, int height,
+                             int stride, uint8_t** output);
+size_t WebPEncodeLosslessRGBA(const uint8_t* rgba, int width, int height,
+                              int stride, uint8_t** output);
+size_t WebPEncodeLosslessBGRA(const uint8_t* bgra, int width, int height,
+                              int stride, uint8_t** output);
+
+Of course in this case, no quality factor is needed since the compression
+occurs without loss of the input values, at the expense of larger output sizes.
+
 Advanced encoding API:
 ----------------------
 

src/enc/picture.c

@@ -1008,7 +1008,8 @@ int WebPPictureDistortion(const WebPPicture* const pic1,
 typedef int (*Importer)(WebPPicture* const, const uint8_t* const, int);
 
 static size_t Encode(const uint8_t* rgba, int width, int height, int stride,
-                     Importer import, float quality_factor, uint8_t** output) {
+                     Importer import, float quality_factor, int lossless,
+                     uint8_t** output) {
   WebPPicture pic;
   WebPConfig config;
   WebPMemoryWriter wrt;
@@ -1019,6 +1020,8 @@ static size_t Encode(const uint8_t* rgba, int width, int height, int stride,
     return 0;  // shouldn't happen, except if system installation is broken
   }
 
+  config.lossless = !!lossless;
+  pic.use_argb_input = !!lossless;
   pic.width = width;
   pic.height = height;
   pic.writer = WebPMemoryWrite;
@@ -1039,7 +1042,7 @@ static size_t Encode(const uint8_t* rgba, int width, int height, int stride,
 #define ENCODE_FUNC(NAME, IMPORTER)                                     \
 size_t NAME(const uint8_t* in, int w, int h, int bps, float q,          \
             uint8_t** out) {                                            \
-  return Encode(in, w, h, bps, IMPORTER, q, out);  \
+  return Encode(in, w, h, bps, IMPORTER, q, 0, out);                    \
 }
 
 ENCODE_FUNC(WebPEncodeRGB, WebPPictureImportRGB);
@@ -1049,6 +1052,19 @@ ENCODE_FUNC(WebPEncodeBGRA, WebPPictureImportBGRA);
 
 #undef ENCODE_FUNC
 
+#define LOSSLESS_DEFAULT_QUALITY 70.
+#define LOSSLESS_ENCODE_FUNC(NAME, IMPORTER)                                 \
+size_t NAME(const uint8_t* in, int w, int h, int bps, uint8_t** out) {       \
+  return Encode(in, w, h, bps, IMPORTER, LOSSLESS_DEFAULT_QUALITY, 1, out);  \
+}
+
+LOSSLESS_ENCODE_FUNC(WebPEncodeLosslessRGB, WebPPictureImportRGB);
+LOSSLESS_ENCODE_FUNC(WebPEncodeLosslessBGR, WebPPictureImportBGR);
+LOSSLESS_ENCODE_FUNC(WebPEncodeLosslessRGBA, WebPPictureImportRGBA);
+LOSSLESS_ENCODE_FUNC(WebPEncodeLosslessBGRA, WebPPictureImportBGRA);
+
+#undef LOSSLESS_ENCODE_FUNC
+
 //------------------------------------------------------------------------------
 
 #if defined(__cplusplus) || defined(c_plusplus)

src/webp/encode.h

@@ -30,6 +30,9 @@ WEBP_EXTERN(int) WebPGetEncoderVersion(void);
 // Returns the size of the compressed data (pointed to by *output), or 0 if
 // an error occurred. The compressed data must be released by the caller
 // using the call 'free(*output)'.
+// These functions compress using the lossy format, and the quality_factor
+// can go from 0 (smaller output, lower quality) to 100 (best quality,
+// larger output).
 WEBP_EXTERN(size_t) WebPEncodeRGB(const uint8_t* rgb,
                                   int width, int height, int stride,
                                   float quality_factor, uint8_t** output);
@@ -43,6 +46,22 @@ WEBP_EXTERN(size_t) WebPEncodeBGRA(const uint8_t* bgra,
                                    int width, int height, int stride,
                                    float quality_factor, uint8_t** output);
 
+// These functions are the equivalent of the above, but compressing in a
+// lossless manner. Files are usually larger than lossy format, but will
+// not suffer any compression loss.
+WEBP_EXTERN(size_t) WebPEncodeLosslessRGB(const uint8_t* rgb,
+                                          int width, int height, int stride,
+                                          uint8_t** output);
+WEBP_EXTERN(size_t) WebPEncodeLosslessBGR(const uint8_t* bgr,
+                                          int width, int height, int stride,
+                                          uint8_t** output);
+WEBP_EXTERN(size_t) WebPEncodeLosslessRGBA(const uint8_t* rgba,
+                                           int width, int height, int stride,
+                                           uint8_t** output);
+WEBP_EXTERN(size_t) WebPEncodeLosslessBGRA(const uint8_t* bgra,
+                                           int width, int height, int stride,
+                                           uint8_t** output);
+
 //------------------------------------------------------------------------------
 // Coding parameters