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VSE: Fix various "off by half a pixel" issues in image transform #116628

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Aras Pranckevicius merged 2 commits from aras_p/blender:vse-fix-filter into main 2024-01-08 16:51:45 +01:00
Conversation 5 Commits 2 Files Changed 1 +18 -13
1 changed files with 18 additions and 13 deletions
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31
source/blender/imbuf/intern/transform.cc
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@ -81,16 +81,12 @@ struct TransformUserData {
void init_add_x(const float4x4 &transform_matrix)
{
const double width = src->x;
add_x = double2(transform_matrix.x_axis()) * width + double2(transform_matrix.location());
add_x = (add_x - start_uv) * (1.0 / width);
add_x = double2(transform_matrix.x_axis());
}
void init_add_y(const float4x4 &transform_matrix)
{
const double height = src->y;
add_y = double2(transform_matrix.y_axis()) * height + double2(transform_matrix.location());
add_y = (add_y - start_uv) * (1.0 / height);
add_y = double2(transform_matrix.y_axis());
}
void init_subsampling(const int num_subsamples)
@ -102,7 +98,7 @@ struct TransformUserData {
for (int y : IndexRange(0, num_subsamples)) {
for (int x : IndexRange(0, num_subsamples)) {
double2 delta_uv = -offset_x - offset_y;
double2 delta_uv = offset_x + offset_y;
delta_uv += x * subsample_add_x;
delta_uv += y * subsample_add_y;
subsampling.delta_uvs.append(delta_uv);
@ -313,6 +309,13 @@ class Sampler {
u = wrap_uv(u, source->x);
v = wrap_uv(v, source->y);
}
/* BLI_bilinear_interpolation functions use `floor(uv)` and `floor(uv)+1`
* texels. For proper mapping between pixel and texel spaces, need to
* subtract 0.5. */
if constexpr (Filter == IMB_FILTER_BILINEAR) {
u -= 0.5f;
v -= 0.5f;
}
if constexpr (Filter == IMB_FILTER_BILINEAR && std::is_same_v<StorageType, float> &&
NumChannels == 4)
{
@ -505,9 +508,10 @@ class ScanlineProcessor {
private:
void process_one_sample_per_pixel(const TransformUserData *user_data, int scanline)
{
double2 uv = user_data->start_uv +
user_data->destination_region.x_range.first() * user_data->add_x +
user_data->add_y * scanline;
/* Note: sample at pixel center for proper filtering. */
double pixel_x = user_data->destination_region.x_range.first() + 0.5;
double pixel_y = scanline + 0.5;
double2 uv = user_data->start_uv + user_data->add_x * pixel_x + user_data->add_y * pixel_y;
output.init_pixel_pointer(user_data->dst,
int2(user_data->destination_region.x_range.first(), scanline));
@ -526,9 +530,10 @@ class ScanlineProcessor {
void process_with_subsampling(const TransformUserData *user_data, int scanline)
{
double2 uv = user_data->start_uv +
user_data->destination_region.x_range.first() * user_data->add_x +
user_data->add_y * scanline;
/* Note: sample at pixel center for proper filtering. */
double pixel_x = user_data->destination_region.x_range.first() + 0.5;
double pixel_y = scanline + 0.5;
double2 uv = user_data->start_uv + user_data->add_x * pixel_x + user_data->add_y * pixel_y;
output.init_pixel_pointer(user_data->dst,
int2(user_data->destination_region.x_range.first(), scanline));