add reading scaled png images

diff --git a/readpng.c b/readpng.c
index d0714ed..08bf80d 100644 (file)
--- a/readpng.c
+++ b/readpng.c
@@ -67,6 +67,43 @@ int readpng(void *dest, const char *fname, readpng_what what, int req_w, int req
 
        switch (what)
        {
+               case READPNG_SCALE:
+               {
+                       int height, width, x_ofs = 0, y_ofs = 0;
+                       unsigned short *dst = dest;
+                       int x_scale, y_scale, x_pos, y_pos; // Q16
+
+                       if (png_get_bit_depth(png_ptr, info_ptr) != 8)
+                       {
+                               lprintf(__FILE__ ": scaled image uses %ibpc, needed 8bpc\n", png_get_bit_depth(png_ptr, info_ptr));
+                               break;
+                       }
+                       width = png_get_image_width(png_ptr, info_ptr);
+                       x_scale = width*65536 / req_w;
+                       height = png_get_image_height(png_ptr, info_ptr);
+                       y_scale = height*65536 / req_h;
+                       if (x_scale < y_scale)
+                               x_scale = y_scale;
+                       else    y_scale = x_scale;
+                       x_ofs = req_w - width*65536 / x_scale;
+                       y_ofs = req_h - height*65536 / y_scale;
+
+                       dst += y_ofs/2*req_w + x_ofs/2;
+                       for (y_pos = 0; y_pos < height*65536; y_pos += y_scale+1)
+                       {
+                               unsigned char *src = row_ptr[y_pos >> 16];
+                               int len = 0;
+                               for (x_pos = 0; x_pos < width*65536; x_pos += x_scale+1, len++)
+                               {
+                                       int o = 3*(x_pos >> 16);
+                                       // TODO: could use bilinear if upsampling?
+                                       *dst++ = PXMAKE(src[o], src[o+1], src[o+2]);
+                               }
+                               dst += req_w - len;
+                       }
+                       break;
+               }
+
                case READPNG_BG:
                {
                        int height, width, h, x_ofs = 0, y_ofs = 0;

diff --git a/readpng.h b/readpng.h
index 4bb7ba7..c3d58a7 100644 (file)
--- a/readpng.h
+++ b/readpng.h
@@ -7,6 +7,7 @@ typedef enum
        READPNG_FONT,
        READPNG_SELECTOR,
        READPNG_24,
+       READPNG_SCALE,
 }
 readpng_what;