//------------------------------------------------------------------------------
// RGBA rescaling
// import new contributions until one row is ready to be output, or all input
// is consumed.
static int Import(byte* src, int src_stride,
int new_lines, WebPRescaler* wrk) {
int num_lines_in = 0;
while (num_lines_in < new_lines && wrk.y_accum > 0) {
ImportRow(src, wrk);
src += src_stride;
++num_lines_in;
wrk.y_accum -= wrk.y_sub;
}
return num_lines_in;
}
//------------------------------------------------------------------------------
// YUV rescaling (no final RGB conversion needed)
static int Rescale(byte* src, int src_stride,
int new_lines, WebPRescaler* wrk) {
int num_lines_out = 0;
while (new_lines-- > 0) { // import new contribution of one source row.
ImportRow(src, wrk);
src += src_stride;
wrk.y_accum -= wrk.y_sub;
while (wrk.y_accum <= 0) { // emit output row(s)
ExportRow(wrk);
++num_lines_out;
}
}
return num_lines_out;
}
static void ImportRow(byte* src,
WebPRescaler* wrk) {
int x_in = 0;
int x_out;
int accum = 0;
if (!wrk.x_expand) {
int sum = 0;
for (x_out = 0; x_out < wrk.dst_width; ++x_out) {
accum += wrk.x_add;
for (; accum > 0; accum -= wrk.x_sub) {
sum += src[x_in++];
}
{ // Emit next horizontal pixel.
int base = src[x_in++];
int frac = base * (-accum);
wrk.frow[x_out] = (sum + base) * wrk.x_sub - frac;
// fresh fractional start for next pixel
sum = MULT(frac, wrk.fx_scale);
}
}
} else { // simple bilinear interpolation
int left = src[0], right = src[0];
for (x_out = 0; x_out < wrk.dst_width; ++x_out) {
if (accum < 0) {
left = right;
right = src[++x_in];
accum += wrk.x_add;
}
wrk.frow[x_out] = right * wrk.x_add + (left - right) * accum;
accum -= wrk.x_sub;
}
}
// Accumulate the new row's contribution
for (x_out = 0; x_out < wrk.dst_width; ++x_out) {
wrk.irow[x_out] += wrk.frow[x_out];
}
}
static void ExportRow(WebPRescaler* wrk) {
int x_out;
int yscale = wrk.fy_scale * (-wrk.y_accum);
assert(wrk.y_accum <= 0);
for (x_out = 0; x_out < wrk.dst_width; ++x_out) {
int frac = MULT(wrk.frow[x_out], yscale);
int v = (int)MULT(wrk.irow[x_out] - frac, wrk.fxy_scale);
wrk.dst[x_out] = (!(v & ~0xff)) ? v : (v < 0) ? 0 : 255;
wrk.irow[x_out] = frac; // new fractional start
}
wrk.y_accum += wrk.y_add;
wrk.dst += wrk.dst_stride;
}
static void InitRescaler(WebPRescaler* wrk,
int src_width, int src_height,
byte* dst,
int dst_width, int dst_height, int dst_stride,
int x_add, int x_sub, int y_add, int y_sub,
int* work) {
wrk.x_expand = (src_width < dst_width);
wrk.src_width = src_width;
wrk.src_height = src_height;
wrk.dst_width = dst_width;
wrk.dst_height = dst_height;
wrk.dst = dst;
wrk.dst_stride = dst_stride;
// for 'x_expand', we use bilinear interpolation
wrk.x_add = wrk.x_expand ? (x_sub - 1) : x_add - x_sub;
wrk.x_sub = wrk.x_expand ? (x_add - 1) : x_sub;
wrk.y_accum = y_add;
wrk.y_add = y_add;
wrk.y_sub = y_sub;
wrk.fx_scale = (1 << RFIX) / x_sub;
wrk.fy_scale = (1 << RFIX) / y_sub;
wrk.fxy_scale = wrk.x_expand ?
((long)dst_height << RFIX) / (x_sub * src_height) :
((long)dst_height << RFIX) / (x_add * src_height);
wrk.irow = work;
wrk.frow = work + dst_width;
}