Exporting Animations from Blender to C++

Exporting animations from Blender to C++ is a multi-step process that requires converting Blender animations into a format that can be easily integrated into a C++ project. This can be achieved by exporting the animation data in a way that it can be read and processed by your C++ application, typically through the use of keyframe data or skeletal animation.

Here’s a step-by-step guide on how to export animations from Blender and use them in C++:

Step 1: Preparing the Animation in Blender

Before exporting the animation, ensure that your animation is set up correctly in Blender. This includes:

• Armatures: If you’re working with skeletal animations, make sure that your armature (skeleton) and rigging are correctly set up.

• Keyframes: Ensure that keyframes for the animation are placed on the correct bones or objects.

• Actions: If your animation uses multiple actions (for example, walking, running, etc.), make sure each action is properly named and configured.

Step 2: Exporting the Animation Data

To export the animation data from Blender, you will need to choose an appropriate file format that C++ can read and work with. Common formats used for exporting 3D animation data include:

2.1. FBX Format

FBX is a widely used format for exporting 3D models and animations. Blender has built-in support for exporting to FBX. Here’s how you can do it:

1. Go to File → Export → FBX (.fbx).

2. In the export settings, make sure to check the Animation box to export keyframes.

3. Adjust other settings depending on your needs (e.g., scale, axis orientation, etc.).

4. Save the file.

Once exported, you will have an .fbx file containing your model and animation.

2.2. GLTF Format

GLTF is another popular format, especially for use in real-time 3D engines. It supports both static and animated meshes. Here’s how you can export it:

1. Go to File → Export → glTF 2.0 (.glb/.gltf).

2. Make sure to enable the Animation export option.

3. Save the file in .gltf or .glb format.

GLTF is lightweight and optimized for real-time applications, so it might be a better choice depending on your C++ engine.

Step 3: Loading and Processing the Animation in C++

After exporting the animation, you need to load it into your C++ application. How you do this will depend on which C++ engine or graphics library you’re using. Here’s an overview for a few common options:

3.1. Using Assimp (Open Source Library)

Assimp is a popular library for importing various 3D model formats into C++. It supports both FBX and GLTF formats. To use Assimp for loading animations:

1. Install Assimp: Download and install Assimp from Assimp’s website.

2. Link Assimp in your project: Make sure you link the Assimp library in your C++ project.

3. Load the Model and Animation:

   cpp
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   #include <assimp/Importer.hpp>
   #include <assimp/scene.h>
   #include <assimp/postprocess.h>
   
   Assimp::Importer importer;
   const aiScene* scene = importer.ReadFile("your_model.fbx", aiProcess_Triangulate | aiProcess_FlipUVs);
   
   if (!scene) {
       std::cerr << "Error loading model: " << importer.GetErrorString() << std::endl;
   }
   

4. Extract Animation Data:
   Assimp allows you to access animation data through the aiAnimation structure. You can loop through all the animations and extract keyframe data for each bone or object.

   cpp
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   aiAnimation* animation = scene->mAnimations[0];
   for (unsigned int i = 0; i < animation->mNumChannels; i++) {
       aiNodeAnim* channel = animation->mChannels[i];
       // Process the keyframes for each bone
   }
   

5. Animate in C++:
   Once you have the keyframe data, you can use this to animate your model in the C++ application by interpolating the transformations (translation, rotation, scale) at each keyframe.

3.2. Using OpenGL

If you are working with OpenGL for rendering in C++, you will have to manually process the exported data from the FBX or GLTF file. Using Assimp as mentioned above can help with loading the data. From there, you can set up shaders to interpolate the bone transformations and apply them to the model.

• Bone Transformations: For skeletal animation, you’ll need to extract the bone transformations (position, rotation, scale) and use them to update the vertex positions in the shader.

• Interpolation: Smoothly interpolate between keyframes based on the current time to animate the bones.

3.3. Using Other Game Engines

If you’re using a game engine like Unreal Engine or Unity, the process of importing Blender animations is a bit different because these engines already have built-in support for common formats (FBX, GLTF, etc.). You can import the FBX or GLTF file directly into the engine and use the built-in animation systems.

In Unreal Engine, for example:

• Importing the FBX: Unreal automatically imports models and animations from FBX files.

• Animation Blueprints: Use Unreal’s animation system to control and play the imported animations.

Step 4: Implementing Animation in C++

Once you’ve successfully loaded the animation data, you will need to implement an animation system in your C++ project. This typically involves:

• Keyframe Interpolation: Interpolate between the positions, rotations, and scales of bones or objects based on the current time.

• Animation Time Management: Track the time of the animation and handle looping, blending, or transitioning between different animations.

• Skinning: If you’re working with skeletal animation, implement bone-based skinning to deform the mesh based on the bone transformations.

Example Code Snippet for Animation Interpolation (Pseudo C++)

Here’s a simplified approach to interpolation between keyframes in C++:

cpp
CopyEdit
// Pseudo code for interpolating position between keyframes
Vec3 interpolatePosition(const aiVector3D& startPos, const aiVector3D& endPos, float timeFraction) {
    return startPos + (endPos - startPos) * timeFraction;
}

// Pseudo code for interpolating rotation (using quaternions)
Quaternion interpolateRotation(const aiQuaternion& startRot, const aiQuaternion& endRot, float timeFraction) {
    return startRot.Slerp(endRot, timeFraction);
}

// Pseudo code for updating the bone transformations based on animation time
void updateBoneTransformations(float animationTime) {
    for (int i = 0; i < numBones; i++) {
        Bone& bone = bones[i];
        
        // Get the keyframes for this bone
        aiNodeAnim* nodeAnim = getNodeAnimation(bone.name);
        
        // Interpolate the position and rotation based on the current time
        float timeFraction = getTimeFraction(animationTime, nodeAnim);
        bone.position = interpolatePosition(nodeAnim->mPosition[0], nodeAnim->mPosition[1], timeFraction);
        bone.rotation = interpolateRotation(nodeAnim->mRotation[0], nodeAnim->mRotation[1], timeFraction);
        
        // Update the final bone transformation matrix
        bone.transformation = computeTransformationMatrix(bone.position, bone.rotation);
    }
}

Conclusion

Exporting animations from Blender to C++ requires exporting the animation data in a format that C++ can understand, such as FBX or GLTF, and then processing that data in your C++ application. Libraries like Assimp make it easier to import the data, and with proper handling of keyframe interpolation and transformations, you can implement smooth animations in your own C++ application or game engine.