Rendering to frame buffer

[SasLuca]

Does anyone have an example of how to render using GlCanvas to a framebuffer?

I tried doing it but for some reason it wouldn't work so I am curious if anyone else has an example.

[hermet]

Hello, please have a look at this api: you can pass your framebuffer id to the id parameter.

    /**
     * @brief Sets the drawing target for rasterization.
     *
     * This function specifies the drawing target where the rasterization will occur. It can target
     * a specific framebuffer object (FBO) or the main surface.
     *
     * @param[in] id The GL target ID, usually indicating the FBO ID. A value of @c 0 specifies the main surface.
     * @param[in] w The width (in pixels) of the raster image.
     * @param[in] h The height (in pixels) of the raster image.
     *
     * @warning This API is experimental and not officially supported. It may be modified or removed in future versions.
     * @warning Drawing on the main surface is currently not permitted. If the identifier (@p id) is set to @c 0, the operation will be aborted.
     *
     * @see Canvas::viewport()
     *
     * @note Currently, this only allows the GL_RGBA8 color space format.
     * @note Experimental API
    */
    Result GlCanvas::target(int32_t id, uint32_t w, uint32_t h) noexcept;

There are plenty of examples in thorvg/examples. You can find out how they create a GL canvas with framebuffer usage.

+ @RuiwenTang

[SasLuca]

Thanks for the reply.

Indeed that api works as intended. My issue is, I am using 2 opengl contexts with a separate one for thorvg, and I couldn't access the framebuffer texture from the thorvg context in my other context.

In my case this was solved by calling SDL_GL_SetAttribute(SDL_GL_SHARE_WITH_CURRENT_CONTEXT, 1); which enables sharing resources between opengl contexts in SDL. Hope this question may be of use to others in the future as well.