Add shadow effect to `libopenshot` #999

aperture147 · 2025-03-21T10:16:44Z

Currently there are no drop shadow effect implemented in libopenshot. To achieve that, people usually do this trick:

Duplicate the clip that requires shadow dropping
Use Brightness effect to make the duplicated clip pitch black
Use Blur effect to make the black clip under looked like a spread out shadow
Place the Clip below and a bit offset of the original clip

This approach has two disadvantages:

Cannot change the color of the shadow: User might want to change the shadow color to a shift the color and no Hue could shift the the color of black
Inconvenient to use: User has to duplicate the clip, rearrange and modify effects on it. This is not an easy task to do if user has more than one Clip to drop shadow (even when managing them programmatically)

My implementation of Shadow effect could solves those disadvantages by two features:

No extra Clip required.
Shadow color could be keyframed. User could change the color freely

Please check this out! All contributions are appreciated!

…r related code

…ss for better encapsulation

…class

… for alpha support

…ties

…nstructor documentation

…ries and improve code clarity

… Shadow effect JSON output

…operties from float to int for consistency

…effect

aperture147 · 2025-03-25T07:10:51Z

This effect uses code from #998, please also check it out @jonoomph!

codecov · 2025-03-25T07:31:38Z

Codecov Report

❌ Patch coverage is 25.17986% with 104 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.35%. Comparing base (47b3081) to head (a239b94).

Files with missing lines	Patch %	Lines
src/effects/Shadow.cpp	0.00%	95 Missing ⚠️
src/Frame.cpp	80.00%	5 Missing ⚠️
src/EffectInfo.cpp	0.00%	3 Missing ⚠️
src/effects/Shadow.h	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #999      +/-   ##
===========================================
- Coverage    59.60%   59.35%   -0.25%     
===========================================
  Files          206      208       +2     
  Lines        20374    20496     +122     
===========================================
+ Hits         12143    12165      +22     
- Misses        8231     8331     +100

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aperture147 · 2025-04-07T08:01:51Z

Hi, this PR is related to #998. Please check it out first. I also included test cases for that pull request!

Copilot

Pull request overview

This PR implements a new Shadow effect for libopenshot, allowing users to add drop shadows to clips with transparent backgrounds without duplicating clips. The implementation provides keyframeable shadow color, position, and blur radius.

Key changes:

New Shadow effect class with support for animated offset, blur radius, and color
Refactored Frame class to add BGRA-aware OpenCV Mat conversion methods
Updated Outline effect to use the new shared Frame methods for BGRA operations

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
src/effects/Shadow.h	Header file defining the Shadow effect class with keyframeable properties
src/effects/Shadow.cpp	Implementation of Shadow effect using OpenCV for alpha-aware shadow rendering
src/Frame.h	Added BGRA OpenCV Mat member and conversion methods for alpha channel support
src/Frame.cpp	Implemented BGRA conversion methods and memory management
src/effects/Outline.h	Refactored to remove duplicate BGRA conversion methods
src/effects/Outline.cpp	Updated to use shared Frame BGRA methods instead of local implementation
tests/CVShadow.cpp	Unit tests for Shadow effect (currently disabled)
tests/Frame.cpp	Added test for BGRA Mat conversion
tests/CMakeLists.txt	Added commented-out Shadow test configuration
src/Effects.h	Registered Shadow effect header
src/EffectInfo.cpp	Added Shadow effect factory and info registration
src/CMakeLists.txt	Added Shadow.cpp to build sources
bindings/python/openshot.i	Exposed Shadow effect to Python bindings

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Copilot · 2025-12-23T08:04:28Z

src/effects/Shadow.cpp

+
+	// Blur the final image to simulate shadow blur. Ignore if blur_radius is 0
+	// FIXME: Not physically correct
+	if (blur_radiusValue > 0.0) {


The condition has an unnecessary floating-point comparison. The variable blur_radiusValue is an integer, so comparing it to 0.0 is inconsistent. Use integer comparison (> 0) instead.

Copilot · 2025-12-23T08:04:28Z

src/effects/Shadow.cpp

+	// The shadow is completely out of the frame
+	if ((abs_x_offset + blur_radiusValue > cv_image.cols) || (abs_y_offset + blur_radiusValue > cv_image.rows)) {
+		return frame;
+	}
+


The logic for checking if the shadow is out of bounds appears incorrect. The condition checks if the absolute offset plus blur radius exceeds the image dimensions, but this doesn't properly account for the shadow position. A shadow offset in the positive direction with blur shouldn't necessarily be considered "completely out of the frame" using this logic. The calculation should consider the actual shadow region relative to the padded canvas and determine if any part of the shadow would be visible in the final frame.

Suggested change

// The shadow is completely out of the frame

if ((abs_x_offset + blur_radiusValue > cv_image.cols) || (abs_y_offset + blur_radiusValue > cv_image.rows)) {

return frame;

}

Copilot · 2025-12-23T08:04:29Z

src/effects/Shadow.cpp

+	cv::Mat shadow_color_mat(cv::Size(paddedWidth, paddedHeight), CV_8UC4, cv::Scalar(redValue, greenValue, blueValue, alphaValue));
+
+	// only shifting image if shadow is not directly under the image
+	if (abs_x_offset && abs_y_offset) {


The condition checking if both offsets are non-zero uses bitwise AND operator instead of logical AND. While 'abs_x_offset && abs_y_offset' works because non-zero values are truthy, the logic suggests this code path should execute only when EITHER offset is non-zero (not both). If the intention is to skip shifting when shadow is directly under the image (both offsets are 0), the condition should be '(abs_x_offset || abs_y_offset)' or 'abs_x_offset != 0 || abs_y_offset != 0' to handle cases where only one offset is zero.

Suggested change

if (abs_x_offset && abs_y_offset) {

if (abs_x_offset != 0 || abs_y_offset != 0) {

Copilot · 2025-12-23T08:04:29Z

src/Frame.cpp

 	audio.reset();
 	#ifdef USE_OPENCV
 	imagecv.release();
+	brga_image_cv.release();


Typo in variable name: should be 'bgra_image_cv' not 'brga_image_cv'. This should match the corrected variable declaration.

Suggested change

brga_image_cv.release();

bgra_image_cv.release();

Copilot · 2025-12-23T08:04:29Z

src/Frame.cpp

+	brga_image_cv = QImage2BGRACvMat(image);
+	return brga_image_cv;
+}
+
+void Frame::SetBGRACvMat(cv::Mat _image) {
+	brga_image_cv = _image;


Typo in variable name: should be 'bgra_image_cv' not 'brga_image_cv'. This should match the corrected variable declaration.

Suggested change

brga_image_cv = QImage2BGRACvMat(image);

return brga_image_cv;

}

void Frame::SetBGRACvMat(cv::Mat _image) {

brga_image_cv = _image;

bgra_image_cv = QImage2BGRACvMat(image);

return bgra_image_cv;

}

void Frame::SetBGRACvMat(cv::Mat _image) {

bgra_image_cv = _image;

Copilot · 2025-12-23T08:04:30Z

tests/CMakeLists.txt

    CVTracker
    CVStabilizer
    CVOutline
+    # CVShadow # Temporally disable CVShadow test


Typo in comment: should be 'Temporarily' not 'Temporally'. 'Temporally' relates to time, while 'temporarily' means for a limited time period.

Suggested change

# CVShadow # Temporally disable CVShadow test

# CVShadow # Temporarily disable CVShadow test

Copilot · 2025-12-23T08:04:31Z

src/Frame.h

+		cv::Mat QImage2BGRACvMat(std::shared_ptr<QImage>& qimage);
+
+		/// Convert OpenCV Mat to QImage (alpha channel included)
+		std::shared_ptr<QImage> BGRACvMat2QImage(cv::Mat img);


Inconsistent naming convention: The method names 'QImage2BGRACvMat' and 'BGRACvMat2QImage' use '2' to mean "to", but the established naming pattern in the codebase is 'Mat2Qimage' which also uses '2'. However, these new methods inconsistently capitalize parts of the name (QImage vs Qimage, CvMat vs nothing). For consistency with the existing 'Mat2Qimage' method, consider naming these 'Qimage2BGRACvMat' and 'BGRACvMat2Qimage' or better yet, use more descriptive names like 'QImageToBGRACvMat' and 'BGRACvMatToQImage' which would be more readable.

Suggested change

cv::Mat QImage2BGRACvMat(std::shared_ptr<QImage>& qimage);

/// Convert OpenCV Mat to QImage (alpha channel included)

std::shared_ptr<QImage> BGRACvMat2QImage(cv::Mat img);

cv::Mat Qimage2BGRACvMat(std::shared_ptr<QImage>& qimage);

/// Convert OpenCV Mat to QImage (alpha channel included)

std::shared_ptr<QImage> BGRACvMat2Qimage(cv::Mat img);

Copilot · 2025-12-23T08:04:31Z

src/Frame.h


 #ifdef USE_OPENCV
 		cv::Mat imagecv; ///< OpenCV image. It will always be in BGR format
+		cv::Mat brga_image_cv; ///< OpenCV image. It will always be in BGR format


The comment incorrectly states this member will be in BGR format, but the variable name and context indicate it should be BGRA format (with alpha channel). The comment should be updated to accurately reflect that this is for BGRA format.

Suggested change

cv::Mat brga_image_cv; ///< OpenCV image. It will always be in BGR format

cv::Mat brga_image_cv; ///< OpenCV image. It will always be in BGRA format (with alpha channel)

Copilot · 2025-12-23T08:04:31Z

src/Frame.h


 #ifdef USE_OPENCV
 		cv::Mat imagecv; ///< OpenCV image. It will always be in BGR format
+		cv::Mat brga_image_cv; ///< OpenCV image. It will always be in BGR format


Typo in variable name: should be 'bgra_image_cv' not 'brga_image_cv'. The letters are transposed, which is inconsistent with the BGRA naming convention used throughout the codebase.

Suggested change

cv::Mat brga_image_cv; ///< OpenCV image. It will always be in BGR format

cv::Mat bgra_image_cv; ///< OpenCV image. It will always be in BGR format

Copilot · 2025-12-23T08:04:31Z

src/effects/Shadow.cpp

+	// The shadow drop directly under the image or completely transparent.
+	// No need to do anything here, return the original frame
+	if (
+		((x_offsetValue == 0.0) && (y_offsetValue == 0) && (blur_radiusValue == 0.0)) // shadow is directly under the image


The condition has unnecessary floating-point comparisons. The variables x_offsetValue, y_offsetValue, and blur_radiusValue are all integers (assigned from GetValue which returns int for these keyframes), so comparing them to floating-point literals like 0.0 is inconsistent. Use integer comparison (== 0) instead.

Suggested change

((x_offsetValue == 0.0) && (y_offsetValue == 0) && (blur_radiusValue == 0.0)) // shadow is directly under the image

((x_offsetValue == 0) && (y_offsetValue == 0) && (blur_radiusValue == 0)) // shadow is directly under the image

aperture147 added 23 commits March 21, 2025 03:14

Add support for alpha channel in image conversion methods and refacto…

a11c9b2

…r related code

Refactor image conversion methods to be member functions of Frame cla…

4551154

…ss for better encapsulation

Add unit test for image conversion with alpha channel support

b020108

Rename imagecv to brga_image_cv for clarity and consistency in Frame …

ed33b6d

…class

Add Shadow effect implementation and corresponding tests

6027f5d

Fix author attribution in Shadow effect class documentation

ab80bd8

Add author attribution and enhance Shadow effect tests

dae3766

Fix author attribution and remove unrelated note

11f8f78

Update author attribution and modify image channel check in unit test…

2520c68

… for alpha support

Update author attribution in Outline effect files for clarity

be5e2e9

Merge branch 'add-bgra-cvmat-converter' into shadow-effect

9d2f082

Release resources for brga_image_cv in Frame destructor

f2f76e0

Merge branch 'add-bgra-cvmat-converter' into shadow-effect

6da48a2

Enhance documentation for Shadow effect to clarify animation capabili…

71d2be9

…ties

Adjust shadow effect alpha value and improve shadow rendering logic

790f5a8

Refactor Shadow effect header to remove unused includes and update co…

944bf0f

…nstructor documentation

Optimize shadow rendering logic to handle edge cases for frame bounda…

f0d415c

…ries and improve code clarity

Fix shadow boundary check to use absolute offsets for improved accuracy

ee01994

Change blur_radius property type from float to int for consistency in…

61302db

… Shadow effect JSON output

updating blur_radius max value to a more reasonable number

95f6a68

Update x_offset and y_offset ranges to -4000 to 4000; change color pr…

c4e3c56

…operties from float to int for consistency

Update file descriptions to reflect Shadow effect instead of Outline …

87d9d61

…effect

Temporarily disable CVShadow test in CMakeLists.txt

bb037c9

aperture147 mentioned this pull request Mar 25, 2025

Add shadow effect icons and document OpenShot/openshot-qt#5734

Open

aperture147 added 3 commits May 25, 2025 15:48

Merge branch 'OpenShot:develop' into shadow-effect

28b46d1

Merge branch 'OpenShot:develop' into shadow-effect

39962f9

Merge branch 'OpenShot:develop' into shadow-effect

461752f

aperture147 added 2 commits July 15, 2025 10:44

Merge branch 'OpenShot:develop' into shadow-effect

b8238bb

Merge branch 'OpenShot:develop' into shadow-effect

a239b94

Copilot AI review requested due to automatic review settings December 23, 2025 07:57

Copilot started reviewing on behalf of aperture147 December 23, 2025 07:57 View session

Copilot AI reviewed Dec 23, 2025

View reviewed changes

	if (abs_x_offset && abs_y_offset) {
	if (abs_x_offset != 0 \|\| abs_y_offset != 0) {

	# CVShadow # Temporally disable CVShadow test
	# CVShadow # Temporarily disable CVShadow test

	cv::Mat brga_image_cv; ///< OpenCV image. It will always be in BGR format
	cv::Mat brga_image_cv; ///< OpenCV image. It will always be in BGRA format (with alpha channel)

	cv::Mat brga_image_cv; ///< OpenCV image. It will always be in BGR format
	cv::Mat bgra_image_cv; ///< OpenCV image. It will always be in BGR format

	((x_offsetValue == 0.0) && (y_offsetValue == 0) && (blur_radiusValue == 0.0)) // shadow is directly under the image
	((x_offsetValue == 0) && (y_offsetValue == 0) && (blur_radiusValue == 0)) // shadow is directly under the image

Add shadow effect to libopenshot #999

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Add shadow effect to `libopenshot` #999

Add shadow effect to `libopenshot` #999

aperture147 commented Mar 21, 2025 •

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