It looks like I have found a solution thanks to someone in the Discord
server. Here is what I changed:
EmscriptenWebGLContextAttributes attrs;
attrs.antialias = true;
attrs.majorVersion = 3;
attrs.minorVersion = 2;
attrs.alpha = true;
attrs.powerPreference = EM_WEBGL_POWER_PREFERENCE_DEFAULT;
// The following lines must be done in exact order, or it will break!
emscripten_webgl_init_context_attributes(&attrs); // you MUST init the
attributes before creating the context
attrs.majorVersion = 3; // you MUST set the version AFTER the above line
EMSCRIPTEN_WEBGL_CONTEXT_HANDLE webgl_context =
emscripten_webgl_create_context("#canvas", &attrs);
emscripten_webgl_make_context_current(webgl_context);
mainContext = SDL_GL_CreateContext(window);
When you modify my main.cpp with this code then it actually shows the game
on the screen and all of the above errors I mentioned disappear. So the
solution is to call emscripten_webgl_init_context_attributes between
creating the attributes and before creating the context. However, if you do
that then it sets up the webgl context using OpenGL ES 2.0 (WebGL 1.0)
which is not what I want (because I would need to change all my shader
code). So that's why you need to set the attributes AGAIN after calling it
(to set majorVersion=3) which results in OpenGL ES 3.0 / WebGL 2.0.
Of course I have no idea WHY any of this needs to be done. I hope this can
either be fixed or documented somewhere with an explanation.
I managed to copy and paste this code into my larger game project and it
worked like a charm. However, I get a different (unrelated) error now which
is that the browser crashes because it runs out of memory... but at least I
can see the game now. The preloaded data file is ~80 MB which isn't huge by
video game standards, but it might be too big for the browser to download.
I did set ALLOW_MEMORY_GROWTH=1 but that didn't seem to prevent the issue.
If anyone can help me out with that too please let me know. Thanks.
On Monday, November 1, 2021 at 9:20:16 AM UTC-5 Floh wrote:
> PS: if you just want to get something on screen in a cross-platform
> application, but don't care if it's SDL2 or GL, check out my sokol headers:
>
> https://floooh.github.io/sokol-html5/
>
> No guarantee that this will protect you from any C++ shenanigans though,
> the headers can be used from C++, but since I prefer plain old C these
> days, most of the sample code is written in C (and the few C++ samples -
> mainly the Dear ImGui stuff - doesn't use the STL).
> On Monday, 1 November 2021 at 15:16:29 UTC+1 Floh wrote:
>
>> I'm also able to reproduce the problem on macOS with Chrome and Safari,
>> but no idea either what's going wrong there.
>>
>> However, I suspect it's not the use of std::string, but that iostream is
>> the culprit, because if I replace std::cout with printf but keep
>> std::string, it works (replacing cout with printf is a good idea anyway,
>> because cout adds an incredible amount of bloat last I checked).
>>
>> On Monday, 1 November 2021 at 12:38:16 UTC+1 [email protected] wrote:
>>
>>> I'm glad someone was able to reproduce it, but that didn't answer any of
>>> my questions.
>>>
>>> I've tried a few more things and maybe the issue is related to strings
>>> in some way. If I add a class that takes a string as a parameter in the
>>> constructor, and then ONLY if I instantiate it, like so:
>>>
>>> class Test
>>> {
>>> public:
>>> Test(std::string test) {} ;
>>> };
>>>
>>> int main()
>>> {
>>> Test test("test");
>>> InitOpenGL(1280, 720, window, mainContext);
>>> BeforeMainLoop();
>>>
>>> return 1;
>>> }
>>>
>>> Then that also results in a black screen. Instantiating a vector of
>>> strings also results in a black screen, like so:
>>> std::vector<std::string> languages = { "english", "japanese" };
>>>
>>> And my original problem with the Log function also happens to involve
>>> strings on some level. If I change the constructor from a string to a const
>>> char* then it works. But changing all instances of strings to const char*
>>> is not ideal (my program needs strings), and I actually tried that with the
>>> Log function and that did not help, so I'm still looking for a solution. So
>>> hopefully this information is helpful for someone to figure out what is
>>> wrong and how to fix it.
>>>
>>>
>>> On Sunday, October 31, 2021 at 12:23:53 AM UTC-5 Shlomi Fish wrote:
>>>
>>>> Hi all!
>>>>
>>>> On Sat, 30 Oct 2021 18:46:19 -0700 (PDT)
>>>> Anton Strickland <[email protected]> wrote:
>>>>
>>>> > I have been stuck on a very simple issue for multiple days and need
>>>> someone
>>>> > who knows what they are doing. I'm trying to use SDL2 and WebGL2
>>>> (OpenGL ES
>>>> > 3) and sometimes it works, but sometimes it doesn't, depending on
>>>> seemingly
>>>> > arbitrary code. Please help. See here for the full details and source
>>>> code:
>>>> >
>>>> >
>>>> https://gist.github.com/AntonStrickland/433c911151ca73826ee679b120fe8d9e
>>>> >
>>>>
>>>> Note that I was able to reproduce the issue on fedora v34 x86-64 with
>>>> firefox:
>>>>
>>>> ```
>>>> System:
>>>> Host: telaviv1.shlomifish.org Kernel: 5.14.14-200.fc34.x86_64 x86_64
>>>> bits: 64 Desktop: Xfce 4.16.0 Distro: Fedora release 34 (Thirty Four)
>>>> CPU:
>>>> Info: Dual Core model: Intel Core i3-2100 bits: 64 type: MT MCP cache:
>>>> L2: 3 MiB
>>>> Speed: 2750 MHz min/max: 1600/3100 MHz Core speeds (MHz): 1: 2750
>>>> 2: 2698 3: 2709 4: 2694
>>>> Graphics:
>>>> Device-1: Intel 2nd Generation Core Processor Family Integrated
>>>> Graphics
>>>> driver: i915 v: kernel Display: x11 server: X.Org 1.20.11 driver:
>>>> loaded:
>>>> modesetting unloaded: fbdev,vesa resolution: 1920x1080~60Hz
>>>> OpenGL: renderer: Mesa DRI Intel HD Graphics 2000 (SNB GT1)
>>>> v: 3.3 Mesa 21.1.8
>>>> ```
>>>>
>>>> As a side note: main.cpp has some trailing whitespace:
>>>> https://perl-begin.org/tutorials/bad-elements/#trailing-whitespace
>>>>
>>>> > Basically, I have a simple program (just over 100 lines of code) that
>>>> > changes the background color of the screen by calling glClear().
>>>> Probably
>>>> > the most basic OpenGL program one can write. When the color is pink,
>>>> that
>>>> > means it's working, and when it's black, it's not working. In the
>>>> above
>>>> > link there is main.cpp which works correctly. I have been doing trial
>>>> and
>>>> > error for this past week commenting out random lines of code to
>>>> isolate the
>>>> > problem, but it seems like changing arbitrary lines of code stops it
>>>> from
>>>> > working. I've noticed that it happens when calling some SDL
>>>> functions, but
>>>> > even just commenting out printing to the console is enough to break
>>>> it. See
>>>> > main.cpp for details.
>>>> >
>>>> > I don't know if this is just an issue with me not understanding how
>>>> this
>>>> > works or if this is an actual bug in emscripten or the SDL port. it's
>>>> > frustrating because when it works, it works all the way (I can use
>>>> shaders
>>>> > and textures to have a working app), but if I change just a tiny
>>>> little
>>>> > thing (even just commenting out an unrelated line of code), suddenly
>>>> > nothing works at all. I have no idea where to even start debugging
>>>> this.
>>>> >
>>>> > I would imagine that there has to be a way to do this since people
>>>> are
>>>> > obviously making WebGL games in C++, but since there are no tutorials
>>>> > online for how to do that it becomes impossible to even set up a
>>>> simple
>>>> > "hello world" script. I purchased a book on how to make games in web
>>>> > assembly but they use the SDL renderer and not OpenGL rendering.
>>>> Other
>>>> > OpenGL web assembly tutorials just use OpenGL without SDL. Surely
>>>> there
>>>> > must be a way to use them together as I have done for my desktop app?
>>>> >
>>>> > I have already reached out on the discord but to no avail so far.
>>>> Someone
>>>> > suggested adding -fsanitize=address when compiling but that actually
>>>> causes
>>>> > the above working code to stop working. I don't really have the time
>>>> to
>>>> > just wait for an answer so I'm hoping this post will get the
>>>> attention of
>>>> > more people.
>>>> >
>>>> > So I know this is getting long, but I'm very confused. Since
>>>> technically by
>>>> > code works, but it's one step away from breaking, and I have no idea
>>>> what
>>>> > that step is or why. My ultimate goal is to copy and paste this code
>>>> into a
>>>> > larger project, but every time I do so, it results in a black screen
>>>> with
>>>> > no indication of what I did wrong.
>>>> >
>>>> > I would like to understand a few things:
>>>> >
>>>> > - Is this a problem with my code, my makefile, SDL, or emscripten?
>>>> > - If this is not a problem with my code, is someone going to fix the
>>>> > issue?
>>>> > - If my desktop code is Open GL 3.3, should I be using OpenGL ES 3 or
>>>> is
>>>> > that part of the problem? And what files do I need to include and
>>>> where do
>>>> > I get them (if what I have isn't correct?)
>>>> > - What is the proper way to set up an emscripten webgl context? My
>>>> > source code includes two different ways of setting it up and I am not
>>>> sure
>>>> > which is correct, even after trial and error.
>>>> > - Can I get someone who is willing to at least compile the code
>>>> > themselves and try out different solutions until they find something
>>>> that
>>>> > can provide an explanation? I don't want someone to suggest adding a
>>>> > single argument to my makefile, and then hours later I get home to
>>>> try it out
>>>> > and realize that it actually causes the program to fail. My program
>>>> is small
>>>> > enough that someone can copy and paste it together, compile it, and
>>>> run it
>>>> > in less than 2 minutes. There is no reason to not do that yourself to
>>>> > check that it works before suggesting a solution to me. I am just a
>>>> little
>>>> > frustrated at this point so please don't take it the wrong way, I
>>>> just
>>>> > want someone to take me seriously so I can move on to the next step
>>>> of my
>>>> > project.
>>>> > - If this mailing list is not the best place to quickly get help like
>>>> > that, who do I need to contact? I am willing to pay for work if that
>>>> needs
>>>> > to be done, but I don't think that should be necessary to get a
>>>> "hello
>>>> > world" program up and running, especially when I've already come this
>>>> far
>>>> > on my own.
>>>> >
>>>> >
>>>> >
>>>>
>>>>
>>>>
>>>> --
>>>>
>>>> Shlomi Fish https://www.shlomifish.org/
>>>> Free (Creative Commons) Music Downloads, Reviews and more -
>>>> https://jamendo.com/
>>>>
>>>> <LeoNerd> “I hear eclipse is really nice, but I’m still waiting for it
>>>> to
>>>> load.”
>>>> — Freenode’s #perl
>>>>
>>>> Please reply to list if it's a mailing list post -
>>>> https://shlom.in/reply .
>>>>
>>>
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