I'm trying to build an overlay for an Android application that uses GLESv2.
I've hooked eglSwapBuffers in order to insert my rending code just before the frame finishes.
I'm able to do simple things like drawing a square with the scissor test:
glEnable(GL_SCISSOR_TEST);
glScissor(0, 0, 200, 200);
glClearColor(1, 0, 0, 1);
glClear(GL_COLOR_BUFFER_BIT);
glDisable(GL_SCISSOR_TEST);
I've also had success drawing simple shapes with the following code, but as soon as I start using vertex attrib pointers the application stops rending correctly and shows a mostly-black screen with a small section that still displays correctly. I'm sure there's some open-gl state that I'm clobbering here but I'm not sure what it is. What would I need to save/restore before/after my draw calls in order to allow the app to continue to render correctly with my overlay?
// Save application state
GLint prev_program;
glGetIntegerv(GL_CURRENT_PROGRAM, &prev_program);
// Do overlay drawing
glUseProgram(program);
glVertexAttribPointer(vPosition, 2, GL_FLOAT, GL_FALSE, 0, RectangleVertices);
glEnableVertexAttribArray(vPosition);
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
glDisableVertexAttribArray(vPosition);
// Trying to restore application state here - there are probably more things that I'm missing.
glUseProgram(prevProgram);