Limit prefilling with color to textures with alpha channel

When loading and preparing a texture we now test the format, and if
the image has an alpha channel we stay on the save side, and always
color the squares before drawing the texture. Only when the format
is not ARGB32 we skip the color fill. (And the default textures
do not have an alpha channel, so at least there no time will be
wasted on pointless color fills.)

diff --git a/draw.c b/draw.c
index 5eb6baa..1d17314 100644 (file)
--- a/draw.c
+++ b/draw.c
@@ -269,7 +269,7 @@ ExposeRedraw (Option *graph, int x, int y, int w, int h)
     cairo_destroy(cr);
 }
 
-static int modV[2], modH[2];
+static int modV[2], modH[2], transparency[2];
 
 static void
 CreatePNGBoard (char *s, int kind)
@@ -288,6 +288,7 @@ CreatePNGBoard (char *s, int kind)
            useTexture |= kind + 1; pngOriginalBoardBitmap[kind] = img;
            w = textureW[kind] = cairo_image_surface_get_width (img);
            h = textureH[kind] = cairo_image_surface_get_height (img);
+           transparency[kind] = cairo_image_surface_get_format (img) == CAIRO_FORMAT_ARGB32;
            n[kind] = 1.; modV[kind] = modH[kind] = -1;
            while((q = strchr(p+1, '-'))) p = q; // find last '-'
            if(strlen(p) < 11 && sscanf(p, "-%dx%d.pn%c", &f, &r, &c) == 3 && c == 'g') {
@@ -754,11 +755,12 @@ DrawLogo (Option *opt, void *logo)
 static void
 BlankSquare (cairo_surface_t *dest, int x, int y, int color, ChessSquare piece, int fac)
 {   // [HGM] extra param 'fac' for forcing destination to (0,0) for copying to animation buffer
-    int x0, y0;
+    int x0, y0, texture = (useTexture & color+1) && CutOutSquare(x, y, &x0, &y0, color);
     cairo_t *cr;
 
     cr = cairo_create (dest);
 
+    if(!texture || transparency[color]) // draw color also (as background) when texture could be transparent
     { // evenly colored squares
        char *col = NULL;
        switch (color) {
@@ -772,7 +774,7 @@ BlankSquare (cairo_surface_t *dest, int x, int y, int color, ChessSquare piece,
        cairo_set_antialias (cr, CAIRO_ANTIALIAS_NONE);
        cairo_fill (cr);
     }
-    if ((useTexture & color+1) && CutOutSquare(x, y, &x0, &y0, color)) {
+    if (texture) {
            cairo_set_source_surface (cr, pngBoardBitmap[color], x*fac - x0, y*fac - y0);
            cairo_set_antialias (cr, CAIRO_ANTIALIAS_NONE);
            cairo_rectangle (cr, x*fac, y*fac, squareSize, squareSize);