<div dir="ltr"><div>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. </div><div>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.</div><div> </div><div>```</div><div><pre style="background-color:rgb(43,43,43);color:rgb(169,183,198);font-family:"JetBrains Mono",monospace;font-size:9.8pt">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; }</pre>``` </div><div>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```. </div><div>The render code is as follows: ``` <pre style="background-color:rgb(43,43,43);color:rgb(169,183,198);font-family:"JetBrains Mono",monospace;font-size:9.8pt">if (texture_type != UNINITIALISED) { switch (texture_type) { case COLOUR: colour_shader.use(); break; </pre><pre style="background-color:rgb(43,43,43);color:rgb(169,183,198);font-family:"JetBrains Mono",monospace;font-size:9.8pt">// other texture type setup </pre><pre style="background-color:rgb(43,43,43);color:rgb(169,183,198);font-family:"JetBrains Mono",monospace;font-size:9.8pt"> 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); }</pre>``` </div><div>Shaders, VAO and VBO set up as follows: ``` <pre style="background-color:rgb(43,43,43);color:rgb(169,183,198);font-family:"JetBrains Mono",monospace;font-size:9.8pt"> 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"); </pre><pre style="background-color:rgb(43,43,43);color:rgb(169,183,198);font-family:"JetBrains Mono",monospace;font-size:9.8pt"> // setup other shaders</pre>``` </div><div>What am I doing wrong?</div></div>