static int ExportAlpha(WebPDecParams* const p, int y_pos, int max_lines_out) {
const WebPRGBABuffer* const buf = &p->output->u.RGBA;
uint8_t* const base_rgba = buf->rgba + y_pos * buf->stride;
const WEBP_CSP_MODE colorspace = p->output->colorspace;
const int alpha_first =
(colorspace == MODE_ARGB || colorspace == MODE_Argb);
uint8_t* dst = base_rgba + (alpha_first ? 0 : 3);
int num_lines_out = 0;
const int is_premult_alpha = WebPIsPremultipliedMode(colorspace);
uint32_t non_opaque = 0;
const int width = p->scaler_a->dst_width;
while (WebPRescalerHasPendingOutput(p->scaler_a) &&
num_lines_out < max_lines_out) {
assert(y_pos + num_lines_out < p->output->height);
WebPRescalerExportRow(p->scaler_a);
non_opaque |= WebPDispatchAlpha(p->scaler_a->dst, 0, width, 1, dst, 0);
dst += buf->stride;
++num_lines_out;
}
if (is_premult_alpha && non_opaque) {
WebPApplyAlphaMultiply(base_rgba, alpha_first,
width, num_lines_out, buf->stride);
}
return num_lines_out;
}
static int ExportAlpha(WebPDecParams* const p, int y_pos) {
const WebPRGBABuffer* const buf = &p->output->u.RGBA;
uint8_t* const base_rgba = buf->rgba + (p->last_y + y_pos) * buf->stride;
const WEBP_CSP_MODE colorspace = p->output->colorspace;
const int alpha_first =
(colorspace == MODE_ARGB || colorspace == MODE_Argb);
uint8_t* dst = base_rgba + (alpha_first ? 0 : 3);
int num_lines_out = 0;
const int is_premult_alpha = WebPIsPremultipliedMode(colorspace);
uint32_t alpha_mask = 0xff;
const int width = p->scaler_a.dst_width;
while (WebPRescalerHasPendingOutput(&p->scaler_a)) {
int i;
assert(p->last_y + y_pos + num_lines_out < p->output->height);
WebPRescalerExportRow(&p->scaler_a);
for (i = 0; i < width; ++i) {
const uint32_t alpha_value = p->scaler_a.dst[i];
dst[4 * i] = alpha_value;
alpha_mask &= alpha_value;
}
dst += buf->stride;
++num_lines_out;
}
if (is_premult_alpha && alpha_mask != 0xff) {
WebPApplyAlphaMultiply(base_rgba, alpha_first,
width, num_lines_out, buf->stride);
}
return num_lines_out;
}
static int EmitAlphaRGB(const VP8Io* const io, WebPDecParams* const p,
int expected_num_lines_out) {
const uint8_t* alpha = io->a;
if (alpha != NULL) {
const int mb_w = io->mb_w;
const WEBP_CSP_MODE colorspace = p->output->colorspace;
const int alpha_first =
(colorspace == MODE_ARGB || colorspace == MODE_Argb);
const WebPRGBABuffer* const buf = &p->output->u.RGBA;
int num_rows;
const int start_y = GetAlphaSourceRow(io, &alpha, &num_rows);
uint8_t* const base_rgba = buf->rgba + start_y * buf->stride;
uint8_t* const dst = base_rgba + (alpha_first ? 0 : 3);
const int has_alpha = WebPDispatchAlpha(alpha, io->width, mb_w,
num_rows, dst, buf->stride);
(void)expected_num_lines_out;
assert(expected_num_lines_out == num_rows);
// has_alpha is true if there's non-trivial alpha to premultiply with.
if (has_alpha && WebPIsPremultipliedMode(colorspace)) {
WebPApplyAlphaMultiply(base_rgba, alpha_first,
mb_w, num_rows, buf->stride);
}
}
return 0;
}
static int EmitAlphaRGB(const VP8Io* const io, WebPDecParams* const p) {
const uint8_t* alpha = io->a;
if (alpha != NULL) {
const int mb_w = io->mb_w;
const WEBP_CSP_MODE colorspace = p->output->colorspace;
const int alpha_first =
(colorspace == MODE_ARGB || colorspace == MODE_Argb);
const WebPRGBABuffer* const buf = &p->output->u.RGBA;
int num_rows;
const int start_y = GetAlphaSourceRow(io, &alpha, &num_rows);
uint8_t* const base_rgba = buf->rgba + start_y * buf->stride;
uint8_t* dst = base_rgba + (alpha_first ? 0 : 3);
uint32_t alpha_mask = 0xff;
int i, j;
for (j = 0; j < num_rows; ++j) {
for (i = 0; i < mb_w; ++i) {
const uint32_t alpha_value = alpha[i];
dst[4 * i] = alpha_value;
alpha_mask &= alpha_value;
}
alpha += io->width;
dst += buf->stride;
}
// alpha_mask is < 0xff if there's non-trivial alpha to premultiply with.
if (alpha_mask != 0xff && WebPIsPremultipliedMode(colorspace)) {
WebPApplyAlphaMultiply(base_rgba, alpha_first,
mb_w, num_rows, buf->stride);
}
}
return 0;
}
