compositing from RGBA to RGBx
compositing against a color from RGBA and storing in a RGBx buffer
+Alpha compositing 8 bit RGBAa onto RGB is defined in terms of
+rounding the exact result (real values in [0,1]):
+
+ cc = ca * aa + (1 - aa) * Cb
+
+ Cc = ROUND [255. * (Ca/255. * Aa/255. + (1 - Aa/255.) * Cb/255.)]
+
+We can comp
+
+ROUND(i / 255.) can be computed exactly for i in [0,255*255] as:
+
+ t = i + 0x80; result = (t + (t >> 8)) >> 8; [ call this as To8(i) ]
+
+So,
+
+ t = Ca * Aa + (255 - Aa) * Cb + 0x80;
+ Cc = (t + (t >> 8)) >> 8;
+
+Alpha compositing 8 bit RaGaBaAa onto RbGbBbAa is a little harder, for
+non-premultiplied alpha. The premultiplied result is simple:
+
+ ac = aa + (1 - aa) * ab
+ cc = ca + (1 - aa) * cb
+
+Which can be computed in integers terms as:
+
+ Cc = Ca + To8 ((255 - Aa) * Cb)
+ Ac = Aa + To8 ((255 - Aa) * Ab)
+
+For non-premultiplied alpha, we need divide the color components by
+the alpha:
+
+ +- (ca * aa + (1 - aa) * ab * cb)) / ac; aa != 0
+ cc = |
+ +- cb; aa == 0
+
+To calculate this as in integer, we note the alternate form:
+
+ cc = cb + aa * (ca - cb) / ac
+
+[ 'cc = ca + (ac - aa) * (cb - ca) / ac' can also be useful numerically,
+ but isn't important here ]
+
+We can express this as integers as:
+
+ Ac_tmp = Aa * 255 + (255 - Aa) * Ab;
+
+ +- Cb + (255 * Aa * (Ca - Cb) + Ac_tmp / 2) / Ac_tmp ; Ca > Cb
+ Cc = |
+ +- Cb - (255 * Aa * (Cb - Ca) + Ac_tmp / 2) / Ac_tmp ; ca <= Cb
+
+Or, playing bit tricks to avoid the conditional
+
+ Cc = Cb + (255 * Aa * (Ca - Cb) + (((Ca - Cb) >> 8) ^ (Ac_tmp / 2)) ) / Ac_tmp
+
TODO
====
the _nearest() variants do it right, most of the other code
is wrong to some degree or another.
- For instance, in composite line, we have:
+ For instance, in composite_line_22_4a4(), we have:
dest[0] = ((0xff0000 - a) * dest[0] + r) >> 24;
- if a is 0, then we have:
+ if a is 0 (implies r == 0), then we have:
- (0xff0000 * dest[0] + r) >> 24
+ (0xff0000 * dest[0]) >> 24
which gives results which are 1 to low:
else
{
unsigned int a1 = 0xff - a0;
-
- dest[0] = (a0 * p[0] + a1 * dest[0]) / 0xff;
- dest[1] = (a0 * p[1] + a1 * dest[1]) / 0xff;
- dest[2] = (a0 * p[2] + a1 * dest[2]) / 0xff;
+ unsigned int tmp;
+
+ tmp = a0 * p[0] + a1 * dest[0] + 0x80;
+ dest[0] = (tmp + (tmp >> 8)) >> 8;
+ tmp = a0 * p[1] + a1 * dest[1] + 0x80;
+ dest[1] = (tmp + (tmp >> 8)) >> 8;
+ tmp = a0 * p[2] + a1 * dest[2] + 0x80;
+ dest[2] = (tmp + (tmp >> 8)) >> 8;
}
break;
}
int *pixel_weights;
pixel_weights = weights + ((x >> (SCALE_SHIFT - SUBSAMPLE_BITS)) & SUBSAMPLE_MASK) * n_x * n_y;
-
+
for (i=0; i<n_y; i++)
{
guchar *q = src[i] + x_scaled * src_channels;
}
#endif /* USE_MMX */
-#ifdef SCALE_LINE_22_33_USED /* This dead code would need changes if we wanted to use it */
static guchar *
scale_line_22_33 (int *weights, int n_x, int n_y,
- guchar *dest, guchar *dest_end, int dest_channels, int dest_has_alpha,
+ guchar *dest, int dest_x, guchar *dest_end, int dest_channels, int dest_has_alpha,
guchar **src, int src_channels, gboolean src_has_alpha,
int x_init, int x_step, int src_width,
int check_size, guint32 color1, guint32 color2)
q0 = src0 + x_scaled * 3;
q1 = src1 + x_scaled * 3;
- pixel_weights = (int *)((char *)weights + ((x >> (SCALE_SHIFT - SUBSAMPLE_BITS - 4)) & (SUBSAMPLE_MASK << 4)));
-
+ pixel_weights = weights + ((x >> (SCALE_SHIFT - SUBSAMPLE_BITS)) & SUBSAMPLE_MASK) * 4;
+
w1 = pixel_weights[0];
w2 = pixel_weights[1];
w3 = pixel_weights[2];
g += w4 * q1[5];
b += w4 * q1[6];
- dest[0] = r >> 16;
- dest[1] = g >> 16;
- dest[2] = b >> 16;
+ dest[0] = (r + 0x8000) >> 16;
+ dest[1] = (g + 0x8000) >> 16;
+ dest[2] = (b + 0x8000) >> 16;
dest += 3;
return dest;
}
-#endif /* SCALE_LINE_22_33_USED */
static void
process_pixel (int *weights, int n_x, int n_y,
for (i = 0; i < n_y; i++)
for (j = 0; j < n_x; j++)
- *(pixel_weights + n_x * i + j) = 65536 * x_weights[j] * x_scale * y_weights[i] * y_scale * overall_alpha;
+ *(pixel_weights + n_x * i + j) = 65536 * x_weights[j] * x_scale * y_weights[i] * y_scale * overall_alpha + 0.5;
}
g_free (x_weights);
g_free (filter.weights);
}
+/**
+ * pixops_composite:
+ * @dest_buf: pointer to location to store result
+ * @render_x0: x0 of region of scaled source to store into @dest_buf
+ * @render_y0: y0 of region of scaled source to store into @dest_buf
+ * @render_x1: x1 of region of scaled source to store into @dest_buf
+ * @render_y1: x1 of region of scaled source to store into @dest_buf
+ * @dest_rowstride: rowstride of @dest_buf
+ * @dest_channels: number of channels in @dest_buf
+ * @dest_has_alpha: whether @dest_buf has alpha
+ * @src_buf: pointer to source pixels
+ * @src_width: width of source (used for clipping)
+ * @src_height: height of source (used for clipping)
+ * @src_rowstride: rowstride of source
+ * @src_channels: number of channels in @src_buf
+ * @src_has_alpha: whether @src_buf has alpha
+ * @scale_x: amount to scale source by in X direction
+ * @scale_y: amount to scale source by in Y direction
+ * @interp_type: type of enumeration
+ * @overall_alpha: overall alpha factor to multiply source by
+ *
+ * Scale source buffer by scale_x / scale_y, then composite a given rectangle
+ * of the result into the destination buffer.
+ **/
void
pixops_composite (guchar *dest_buf,
int render_x0,
break;
}
+ if (filter.n_x == 2 && filter.n_y == 2 && dest_channels == 3 && src_channels == 3)
+ {
#ifdef USE_MMX
- if (filter.n_x == 2 && filter.n_y == 2 &&
- found_mmx && dest_channels == 3 && src_channels == 3)
- line_func = scale_line_22_33_mmx_stub;
+ if (found_mmx)
+ line_func = scale_line_22_33_mmx_stub;
+ else
+#endif
+ line_func = scale_line_22_33;
+ }
else
-#endif
line_func = scale_line;
pixops_process (dest_buf, render_x0, render_y0, render_x1, render_y1,
cmpl %esi,28(%ebp)
je .out
+/* For the body of this loop, %mm01, %mm1, %mm2, %mm3 hold the 4 adjoining
+ * points we are interpolating between, as:
+ *
+ * 000000BB00GG00RR
+ */
+
/* Load initial values into %mm1, %mm3 */
leal (%edx,%edx,2),%edx # Multiply by 3
jmp .newx
.p2align 4,,7
.loop:
-/* int x_index = (x & 0xf000) >> 12 */
+/* short *pixel_weights = weights + ((x >> (SCALE_SHIFT - SUBSAMPLE_BITS)) & SUBSAMPLE_MASK) * n_x * n_y
+ * 16 4 0xf 2 2
+ */
movl %ebx,%eax
andl $0xf000,%eax
shrl $7,%eax
+/* At this point, %edi holds weights. Load the 4 weights into %mm4,%mm5,%mm6,%mm7, multiply and
+ * accumulate.
+ */
movq (%edi,%eax),%mm4
pmullw %mm0,%mm4
movq 8(%edi,%eax),%mm5
paddw %mm6, %mm7
paddw %mm5, %mm7
+/* %mm7 holds the accumulated sum. Compute (C + 0x80) / 256
+ */
+ pxor %mm4, %mm4
+ movl $8421504, %eax # 0x00808080
+ movd %eax, %mm6
+ punpcklbw %mm4, %mm6
+ paddw %mm6, %mm7
psrlw $8, %mm7
+
+/* Pack into %eax and store result
+ */
packuswb %mm7, %mm7
movd %mm7, %eax
/* x += x_step; */
addl 24(%ebp),%ebx
-/* x_scale = x >> 16; */
+/* x_scaled = x >> 16; */
movl %ebx,%edx
sarl $16,%edx
leal (%edx,%edx,2),%edx # Multiply by 3
movl 16(%ebp),%edi
- pxor %mm4, %mm4
movzbl 2(%edi,%edx),%ecx
shll $16,%ecx
movzwl (%edi,%edx),%eax
projects / gtk4.git / commitdiff