GlImageSink Callback Issue

[Edward Anon]

Could you expand on 1 and 2?
This rendering code works with my single threaded application.

Is the problem with 1 the fact that the vertices are allocated inside a
function (ie on the stack)?
I have no idea what you mean by 2. Apologies for being a noob.
Re 3, does this mean gstreamer creates a separate OpenGL context? Is there
a new context made for every element? Do some elements share contexts?

Thanks

On Mon, Aug 2, 2021 at 3:40 AM Matthew Waters <ystreet00 at gmail.com> wrote:

> Take a look at
>
>
> https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/blob/master/gst-libs/gst/gl/gstglfilter.c#L1165
> .
>
> I can notice a couple of things wrong:
> 1. Vertex glBufferData call is taking the address of an array that should
> not be taken.
> 2. No retrieval of the vertex attribute locations (GPU driver decides
> these)
> 3. You may not be creating the VAO in the correct thread? VAO's are not
> OpenGL shareable resource across OpenGL contexts.
>
> Cheers
> -Matt
>
> On 2/8/21 5:47 am, Edward Anon via gstreamer-devel wrote:
>
> My client takes a camera feed over RTP. I want to render an overlay onto
> it using opengl.  Hence, I want to use GlImageSink in my application as it
> provides me with the next frame already in a texture. I want to blit the
> already rendered overlay onto the texture prior to rendering.
>
> As a first step I am writing a simple draw callback which should just
> render the texture to the screen. I am basing my callback on the cube
> example in the gst-plugins-base source.
>
> ```
>
> gboolean drawCallback (GstElement * gl_sink, GstGLContext *context, GstSample * sample, gpointer data) {
>   assert(gl_sink); assert(context); assert(sample); assert(not data);  GstVideoFrame v_frame;  GstVideoInfo v_info;  GstBuffer *buf = gst_sample_get_buffer (sample);  GstCaps *caps = gst_sample_get_caps (sample);  gst_video_info_from_caps (&v_info, caps);  if (!gst_video_frame_map (&v_frame, &v_info, buf, (GstMapFlags) (GST_MAP_READ | GST_MAP_GL))) {
>       g_warning ("Failed to map the video buffer");      return TRUE;  }
>
>   GLuint texture_id = *(guint *) v_frame.data[0];  Texture t; t.from(texture_id, Texture::TextureType::COLOUR);  t.render();  return true;}
>
> ```
>
> However, I get the following error: ```gldebug
> gstgldebug.c:306:_gst_gl_debug_callback:<glcontextglx0> high: GL error from
> API id:1, GL_INVALID_OPERATION in glDrawArrays```.
>
> The render code is as follows:
> ```
>
> if (texture_type != UNINITIALISED) {
>   switch (texture_type) {
>   case COLOUR:
>     colour_shader.use();    break;
>
> // other texture type setup
>
>   default:
>     throw std::runtime_error("Unsupported texture type");  }
>
>   glBindVertexArray(quadVAO);  glDisable(GL_DEPTH_TEST);  glBindTexture(GL_TEXTURE_2D, opengl_texture);  glDrawArrays(GL_TRIANGLES, 0, 6);  glBindTexture(GL_TEXTURE_2D, 0);  glEnable(GL_DEPTH_TEST);}
>
> ```
> Shaders, VAO and VBO set up as follows:
> ```
>
>     glGenVertexArrays(1, &quadVAO);    glBindVertexArray(quadVAO);    glGenBuffers(1, &quadVBO);    glBindBuffer(GL_ARRAY_BUFFER, quadVBO);    glBindVertexArray(quadVAO);    glBindBuffer(GL_ARRAY_BUFFER, quadVBO);    glEnableVertexAttribArray(0);    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(float),                          (void *)nullptr);    glEnableVertexAttribArray(1);    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(float),                          (void *)(2 * sizeof(float)));    constexpr float quadVertices[] = {
>         // positions   // texCoords        1.0f, -1.0f,  0,  1,    // top left        1.0f, 1.0f, 0,  0,      // bottom left        -1.0f,  1.0f, 1,  0,    // bottom right        1.0f, -1.0f,  0,  1,    // top left        -1.0f, 1.0f,  1,  0,    // bottom right        -1.0f, -1.0f, 1,  1     // top right    };    glBufferData(GL_ARRAY_BUFFER, sizeof(quadVertices), &quadVertices,                 GL_STATIC_DRAW);    glBindVertexArray(0);    colour_shader = Shader(shaderRoot + "quadFromTexture.vs",                           shaderRoot + "colourTexture.fs");
>
>     // setup other shaders
>
> ```
>
> What am I doing wrong?
>
>
>
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