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UI: Preserve position during alignment change #4734

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27 changes: 26 additions & 1 deletion UI/window-basic-transform.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -52,7 +52,7 @@ OBSBasicTransform::OBSBasicTransform(OBSBasic *parent)
HookWidget(ui->rotation, DSCROLL_CHANGED, SLOT(OnControlChanged()));
HookWidget(ui->sizeX, DSCROLL_CHANGED, SLOT(OnControlChanged()));
HookWidget(ui->sizeY, DSCROLL_CHANGED, SLOT(OnControlChanged()));
HookWidget(ui->align, COMBO_CHANGED, SLOT(OnControlChanged()));
HookWidget(ui->align, COMBO_CHANGED, SLOT(OnAlignmentChanged()));
HookWidget(ui->boundsType, COMBO_CHANGED, SLOT(OnBoundsType(int)));
HookWidget(ui->boundsAlign, COMBO_CHANGED, SLOT(OnControlChanged()));
HookWidget(ui->boundsWidth, DSCROLL_CHANGED, SLOT(OnControlChanged()));
Expand Down Expand Up @@ -251,6 +251,7 @@ void OBSBasicTransform::RefreshControls()
int boundsAlignIndex = AlignToList(osi.bounds_alignment);

ignoreItemChange = true;

ui->positionX->setValue(osi.pos.x);
ui->positionY->setValue(osi.pos.y);
ui->rotation->setValue(osi.rot);
Expand All @@ -267,6 +268,9 @@ void OBSBasicTransform::RefreshControls()
ui->cropRight->setValue(int(crop.right));
ui->cropTop->setValue(int(crop.top));
ui->cropBottom->setValue(int(crop.bottom));

oti_save = osi;
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@PatTheMav PatTheMav Jan 10, 2024

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Please use a more informative variable name here and use camelCase instead (we tend to prefer camelCase for C++ and ObjC and snake_case for pure C).


ignoreItemChange = false;

std::string name = obs_source_get_name(source);
Expand Down Expand Up @@ -324,9 +328,30 @@ void OBSBasicTransform::OnControlChanged()

ignoreTransformSignal = true;
obs_sceneitem_set_info(item, &oti);
oti_save = oti;
ignoreTransformSignal = false;
}

void OBSBasicTransform::OnAlignmentChanged()
{
if (ignoreItemChange)
return;

uint32_t newAlignment = listToAlign[ui->align->currentIndex()];
struct vec2 offset;

obs_sceneitem_alignment_get_vecdiff(item, &offset, oti_save.alignment,
newAlignment);

ignoreItemChange = true;

ui->positionX->setValue(oti_save.pos.x + offset.x);
ui->positionY->setValue(oti_save.pos.y + offset.y);

ignoreItemChange = false;
OnControlChanged();
}

void OBSBasicTransform::OnCropChanged()
{
if (ignoreItemChange)
Expand Down
2 changes: 2 additions & 0 deletions UI/window-basic-transform.hpp
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Expand Up @@ -23,6 +23,7 @@ class OBSBasicTransform : public QDialog {
OBSSignal deselectSignal;

std::string undo_data;
obs_transform_info oti_save;

bool ignoreTransformSignal = false;
bool ignoreItemChange = false;
Expand All @@ -44,6 +45,7 @@ private slots:
void SetItemQt(OBSSceneItem newItem);
void OnBoundsType(int index);
void OnControlChanged();
void OnAlignmentChanged();
void OnCropChanged();
void on_resetButton_clicked();

Expand Down
7 changes: 7 additions & 0 deletions docs/sphinx/reference-scenes.rst
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Expand Up @@ -458,6 +458,13 @@ Scene Item Functions

---------------------

.. function:: void obs_sceneitem_alignment_get_vecdiff(const obs_sceneitem_t *item, struct vec2 *offset, uint32_t align_from, uint32_t align_to)

Gets the positional difference when switching between different alignment
settings for the scene item.

---------------------

.. function:: void obs_sceneitem_get_draw_transform(const obs_sceneitem_t *item, struct matrix4 *transform)

Gets the transform matrix of the scene item used for drawing the
Expand Down
57 changes: 51 additions & 6 deletions libobs/obs-scene.c
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@
#include "graphics/math-defs.h"
#include "obs-scene.h"
#include "obs-internal.h"
#include <math.h>

const struct obs_source_info group_info;

Expand Down Expand Up @@ -358,7 +359,7 @@ void add_alignment(struct vec2 *v, uint32_t align, int cx, int cy)
v->y += (float)(cy / 2);
}

static void calculate_bounds_data(struct obs_scene_item *item,
static void calculate_bounds_data(const struct obs_scene_item *item,
struct vec2 *origin, struct vec2 *scale,
uint32_t *cx, uint32_t *cy)
{
Expand Down Expand Up @@ -431,8 +432,6 @@ static void update_item_transform(struct obs_scene_item *item, bool update_tex)
struct vec2 base_origin;
struct vec2 origin;
struct vec2 scale;
struct calldata params;
uint8_t stack[128];

if (os_atomic_load_long(&item->defer_update) > 0)
return;
Expand Down Expand Up @@ -499,9 +498,13 @@ static void update_item_transform(struct obs_scene_item *item, bool update_tex)

/* ----------------------- */

calldata_init_fixed(&params, stack, sizeof(stack));
calldata_set_ptr(&params, "item", item);
signal_parent(item->parent, "item_transform", &params);
if (item->parent) {
struct calldata params;
uint8_t stack[128];
calldata_init_fixed(&params, stack, sizeof(stack));
calldata_set_ptr(&params, "item", item);
signal_parent(item->parent, "item_transform", &params);
}

if (!update_tex)
return;
Expand Down Expand Up @@ -2733,6 +2736,48 @@ void obs_sceneitem_set_info(obs_sceneitem_t *item,
}
}

void obs_sceneitem_alignment_get_vecdiff(const obs_sceneitem_t *item,
struct vec2 *offset,
uint32_t align_from, uint32_t align_to)
{
if (!item || !offset)
return;

// Mathematical background based on update_item_transform:
// matrix4 children seen as rows (implied in matrix multiply function):
// T_i = Eye(4) * M_Scale * M_Align_i^(-1) * M_Rot * M_Pos_i
// Original alignment transformation:
// T_1 (stored in mat_T1)
// = Eye(4) * M_Scale * M_Align_1^(-1) * M_Rot * M_Pos_1
// New alignment transformation without position adaptation:
// T_2* (stored in mat_T2_star)
// = Eye(4) * M_Scale * M_Align_2^(-1) * M_Rot * M_Pos_1
// New whole transformation should be equal to previous
// T_2 = T_2* * M_pos_12 =? T_1
// ->
// M_pos_12 = (T_2*)^(-1) * T_1

struct matrix4 mat_T1, mat_T2_star, mat_t12;
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@PatTheMav PatTheMav Jan 10, 2024

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Do not use comma-based declaration, you can also write out matrix in the variable names (using matrix_T1 itself is ok because it follows the formulas in the comment above).

I also think it should be ok to disable clang-format for that comment block to make the formulas more readable.


obs_sceneitem_t temp_item = *item;

// prevent signals to be sent to the scene
temp_item.parent = NULL;

temp_item.align = align_from;
update_item_transform(&temp_item, false);
obs_sceneitem_get_draw_transform(&temp_item, &mat_T1);

temp_item.align = align_to;
update_item_transform(&temp_item, false);
obs_sceneitem_get_draw_transform(&temp_item, &mat_T2_star);
matrix4_inv(&mat_T2_star, &mat_T2_star);

matrix4_mul(&mat_t12, &mat_T2_star, &mat_T1);

vec2_set(offset, mat_t12.t.x, mat_t12.t.y);
}

void obs_sceneitem_get_draw_transform(const obs_sceneitem_t *item,
struct matrix4 *transform)
{
Expand Down
5 changes: 4 additions & 1 deletion libobs/obs.h
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Expand Up @@ -1819,7 +1819,10 @@ EXPORT void obs_sceneitem_get_info(const obs_sceneitem_t *item,
struct obs_transform_info *info);
EXPORT void obs_sceneitem_set_info(obs_sceneitem_t *item,
const struct obs_transform_info *info);

EXPORT void obs_sceneitem_alignment_get_vecdiff(const obs_sceneitem_t *item,
struct vec2 *offset,
uint32_t align_from,
uint32_t align_to);
EXPORT void obs_sceneitem_get_draw_transform(const obs_sceneitem_t *item,
struct matrix4 *transform);
EXPORT void obs_sceneitem_get_box_transform(const obs_sceneitem_t *item,
Expand Down