On 02/04/2016 02:47 AM, Oded Gabbay wrote:
On Tue, Feb 2, 2016 at 8:28 AM, <[email protected]> wrote:
From: Bill Spitzak <[email protected]>
If a negative value is used for the subsampling, then -n subsamples are
used at scale==1, and fewer are used at larger scale, more are used at
smaller scale, so that the total number of samples is approximately
the same. The computed value is rounded up to the next power of 2.
The scale demo is modified to allow these negative numbers, and initially
uses -12.
Signed-off-by: Bill Spitzak <[email protected]>
---
demos/scale.ui | 5 +++--
pixman/pixman-filter.c | 24 ++++++++++++++++++++++++
2 files changed, 27 insertions(+), 2 deletions(-)
diff --git a/demos/scale.ui b/demos/scale.ui
index b62cbfb..1e77f56 100644
--- a/demos/scale.ui
+++ b/demos/scale.ui
@@ -24,12 +24,12 @@
<property name="page_size">10</property>
</object>
<object class="GtkAdjustment" id="subsample_adjustment">
- <property name="lower">0</property>
+ <property name="lower">-256</property>
<property name="upper">12</property>
<property name="step_increment">1</property>
<property name="page_increment">1</property>
<property name="page_size">0</property>
- <property name="value">4</property>
+ <property name="value">-12</property>
</object>
<object class="GtkWindow" id="main">
<child>
@@ -321,6 +321,7 @@
<object class="GtkSpinButton"
id="subsample_spin_button">
<property name="visible">True</property>
<property
name="adjustment">subsample_adjustment</property>
+ <property name="value">-12</property>
</object>
<packing>
<property name="left_attach">1</property>
diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c
index f28cc29..6e8024a 100644
--- a/pixman/pixman-filter.c
+++ b/pixman/pixman-filter.c
@@ -342,14 +342,38 @@ filter_width(pixman_kernel_t reconstruct, pixman_kernel_t
sample,
double* size, int* subsample_bits)
{
int width;
+ /* IMPULSE.x does not work for size < 1.0 */
if (reconstruct == PIXMAN_KERNEL_IMPULSE && *size < 1.0)
*size = 1.0;
+ /* Convolution adds the widths of the filters together */
width = ceil (filters[reconstruct].width + *size * filters[sample].width);
+ /* If there will only be one sample, it must be 1.0 due to normalization,
+ and subsampling is useless. */
if (width <= 1)
{
width = 1;
*subsample_bits = 0;
}
+ else if (*subsample_bits < 0)
+ {
+ /* The intention was to do -n / size rounded up to the next power of 2,
+ but this non-linear function seems to work better. For large size
+ it is the width of the BOX.BOX filter. For small size it reduces
+ samples by 2 at maximum. */
+ double desired_samples = -*subsample_bits;
+ if (sample == PIXMAN_KERNEL_IMPULSE)
+ ; /* For x.IMPULSE no scaling is done */
+ else if (*size >= 1.0)
+ desired_samples *= 2.0 / (*size + 1.0);
+ else
+ desired_samples *= 2.0 / ((*size + 1.0) * *size);
+ *subsample_bits = (int) ceil (log2(desired_samples) - .01);
+ if (*subsample_bits < 0)
+ *subsample_bits = 0;
+ else if (*subsample_bits > 8)
+ /* Assume we cannot see more than 256 different shades and limit
subsampling */
+ *subsample_bits = 8;
+ }
return width;
}
--
1.9.1
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I tried applying just the first hunk (the scale.ui change) without the
second hunk to see If I get any visual errors in scale demo, but
couldn't see anything wrong. So, I would need to see some form of
test/example that is affected by this patch, as I don't have the
knowledge to even ACK it.
Otherwise, you will need to get someone else to review this (Soren ?).
Oded
Run it with the graph output and you will see that the new one produces
far fewer subsamples and changes the number of them as the scale changes.
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