feat(vm): add show_error function by emiyl · Pull Request #353 · ButterscotchRunner/Butterscotch

emiyl · 2026-07-24T22:36:39Z

Adds in the debug show_error function. In GameMaker, this would open a popup window but due to this project needing to support multiple frontends, I've just made it print the error instead and optionally exit the game if the game marks it necessary.

When this is called: show_error("Assertion failed: " + _msg, true);, the following is output:

Game error: Assertion failed: vertex_format_end returned invalid format
Game aborted due to show_error() call.

and the game quits.

emiyl · 2026-07-24T23:03:04Z

Added desktop popups for Windows and macOS on all backends, and for Linux on SDL2 and SDL3. I haven't tested Windows or Linux but I think it should work.

For GLFW and SDL1, macOS and Windows use the native system calls to show an error message. This functionality is included in SDL2 and SDL3 though, so we can just use that.

Un1q32 · 2026-07-24T23:08:58Z

Do we need a dedicated Mac thing? Doesn't glfw have a message box function we can use instead? Also we would need a ton of modification to the build system to add objective C because the makefile is only setup to build .c files. My iOS port handled this by building everything with -ObjC and just putting the objc in a .c file but idk if that would work well with cmake.

emiyl · 2026-07-24T23:10:57Z

Makefile modification is minimal:

if(APPLE AND CMAKE_SYSTEM_NAME STREQUAL "Darwin")
    target_sources(butterscotch PRIVATE src/desktop/backends/platform/macos.m)
    find_library(COCOA_LIBRARY Cocoa REQUIRED)
    target_link_libraries(butterscotch PRIVATE ${COCOA_LIBRARY})
endif()

As far as I can tell, GLFW and SDL1 do not have error popup functions.

Un1q32 · 2026-07-24T23:11:34Z

Honestly if glfw doesn't have a message box API then maybe it would be better to just phone it in and call printf and not have a popup then to deal with objc, unless there's some super clean way to do it I haven't thought of. Maybe we could just tell cmake to always pass -ObjC

Un1q32 · 2026-07-24T23:12:12Z

Makefile modification is minimal:
if(APPLE)
    target_sources(butterscotch PRIVATE src/desktop/backends/platform/macos.m)
    find_library(COCOA_LIBRARY Cocoa REQUIRED)
    target_link_libraries(butterscotch PRIVATE ${COCOA_LIBRARY})
endif()
As far as I can tell, GLFW and SDL1 do not have error popup functions.

That code block is cmake not make

emiyl · 2026-07-24T23:13:54Z

Isn't cmake used to build the project? I don't see what's particularly problematic about this implementation. I guess it's possible to do it in pure C using the objc runtime but I don't think it's necessary - it's not hard to compile objc and it only affects macOS.

Un1q32 · 2026-07-24T23:15:40Z

Isn't cmake used to build the project? I don't see what's particularly problematic about this implementation. I guess it's possible to do it in pure C using the objc runtime but I don't think it's necessary - it's not hard to compile objc and it only affects macOS.

We also have a makefile build for legacy systems that can't run cmake easily, and stuff with weird incomplete C libraries. I guess we could add some of the incomplete C library stuff to cmake too but I haven't bothered.

emiyl · 2026-07-24T23:15:48Z

fwiw it does also print to console no matter what, the popup is just a nice bonus

emiyl · 2026-07-24T23:16:09Z

We also have a makefile build for legacy systems that can't run cmake easily, and stuff with weird incomplete C libraries. I guess we could add some of the incomplete C library stuff to cmake too but I haven't bothered.

i guess but this wouldn't affect those systems surely

Un1q32 · 2026-07-24T23:17:50Z

The makefile build also supports modern stuff that uses the desktop backend. I use it over cmake because it lets me skip actually running cmake before I can run make.

emiyl · 2026-07-24T23:18:29Z

fair enough, let me see if i can update the makefile too

Un1q32 · 2026-07-24T23:19:14Z

I eventually wanna make the makefile build support all platforms. I don't want to drop macOS support from the makefile, especially when old macOS versions are a key use case for the makefile.

emiyl · 2026-07-24T23:22:22Z

Would adding this into the Makefile in the GLFW3, GLFW2 and SDL1 if statements not work?

ifeq ($(OS),Darwin)
SRCS += src/desktop/backends/platform/macos.m
LIBS += -framework Cocoa
endif

Makefile doesn't work for me and i cba figure out why but that should be fine surely

emiyl · 2026-07-24T23:29:26Z

okay i figured out why it wasn't working and now it's all fixed and it all works yay

Un1q32 · 2026-07-24T23:30:41Z

I don't want to duplicate the compile rule is the issue

Un1q32 · 2026-07-24T23:31:55Z

Can you just put it in a .c file and pass -ObjC on Darwin, put it in a header that's guarded by #ifdef __APPLE__

emiyl · 2026-07-24T23:32:56Z

how about this? no duplicate compiler rule there

emiyl · 2026-07-24T23:33:56Z

the issue with just putting it as a C file is that then

#import <Cocoa/Cocoa.h>

void show_error_box(const char *message)
{
    @autoreleasepool {
        NSAlert *alert = [[NSAlert alloc] init];

        [alert setMessageText:@"Error"];
        [alert setInformativeText:
            [NSString stringWithUTF8String:message]];

        [alert addButtonWithTitle:@"OK"];
        [alert setAlertStyle:NSAlertStyleCritical];

        [alert runModal];
    }
}

becomes

#include <stdio.h>
#include <objc/objc.h>
#include <objc/runtime.h>
#include <objc/message.h>

static id send_id(id obj, SEL sel)
{
    return ((id (*)(id, SEL))objc_msgSend)(obj, sel);
}

static id send_id_id(id obj, SEL sel, id arg)
{
    return ((id (*)(id, SEL, id))objc_msgSend)(obj, sel, arg);
}

static void send_void_id(id obj, SEL sel, id arg)
{
    ((void (*)(id, SEL, id))objc_msgSend)(obj, sel, arg);
}

static void send_void_int(id obj, SEL sel, int arg)
{
    ((void (*)(id, SEL, int))objc_msgSend)(obj, sel, arg);
}

void show_error_box(const char *message)
{
    Class NSAlert = (Class)objc_getClass("NSAlert");
    Class NSString = (Class)objc_getClass("NSString");

    id alert = send_id(send_id((id)NSAlert, sel_registerName("alloc")),
                       sel_registerName("init"));

    id title = send_id_id((id)NSString,
                          sel_registerName("stringWithUTF8String:"),
                          (id)"Error");

    id text = send_id_id((id)NSString,
                         sel_registerName("stringWithUTF8String:"),
                         (id)message);

    send_void_id(alert, sel_registerName("setMessageText:"), title);
    send_void_id(alert, sel_registerName("setInformativeText:"), text);

    id ok = send_id_id((id)NSString,
                       sel_registerName("stringWithUTF8String:"),
                       (id)"OK");

    send_id_id(alert, sel_registerName("addButtonWithTitle:"), ok);
    send_void_int(alert, sel_registerName("setAlertStyle:"), 2);

    send_id(alert, sel_registerName("runModal"));
}

one of those is a lot more maintainable and readable

Un1q32 · 2026-07-24T23:35:13Z

Oh shit does that work? I spent way too fuckin long tryna figure out a way to do that when doing iOS. Good shit.

emiyl · 2026-07-24T23:35:26Z

🫡

Un1q32 · 2026-07-24T23:37:32Z

the issue with just putting it as a C file is that then

#import <Cocoa/Cocoa.h>

void show_error_box(const char *message)
{
    @autoreleasepool {
        NSAlert *alert = [[NSAlert alloc] init];

        [alert setMessageText:@"Error"];
        [alert setInformativeText:
            [NSString stringWithUTF8String:message]];

        [alert addButtonWithTitle:@"OK"];
        [alert setAlertStyle:NSAlertStyleCritical];

        [alert runModal];
    }
}

becomes

#include <stdio.h>
#include <objc/objc.h>
#include <objc/runtime.h>
#include <objc/message.h>

static id send_id(id obj, SEL sel)
{
    return ((id (*)(id, SEL))objc_msgSend)(obj, sel);
}

static id send_id_id(id obj, SEL sel, id arg)
{
    return ((id (*)(id, SEL, id))objc_msgSend)(obj, sel, arg);
}

static void send_void_id(id obj, SEL sel, id arg)
{
    ((void (*)(id, SEL, id))objc_msgSend)(obj, sel, arg);
}

static void send_void_int(id obj, SEL sel, int arg)
{
    ((void (*)(id, SEL, int))objc_msgSend)(obj, sel, arg);
}

void show_error_box(const char *message)
{
    Class NSAlert = (Class)objc_getClass("NSAlert");
    Class NSString = (Class)objc_getClass("NSString");

    id alert = send_id(send_id((id)NSAlert, sel_registerName("alloc")),
                       sel_registerName("init"));

    id title = send_id_id((id)NSString,
                          sel_registerName("stringWithUTF8String:"),
                          (id)"Error");

    id text = send_id_id((id)NSString,
                         sel_registerName("stringWithUTF8String:"),
                         (id)message);

    send_void_id(alert, sel_registerName("setMessageText:"), title);
    send_void_id(alert, sel_registerName("setInformativeText:"), text);

    id ok = send_id_id((id)NSString,
                       sel_registerName("stringWithUTF8String:"),
                       (id)"OK");

    send_id_id(alert, sel_registerName("addButtonWithTitle:"), ok);
    send_void_int(alert, sel_registerName("setAlertStyle:"), 2);

    send_id(alert, sel_registerName("runModal"));
}

one of those is a lot more maintainable and readable

Oh no my idea was literally having objc in a .c file, not writing actual C. If you pass -ObjC to the compiler it will still work. Having .m files is better tho so if there's no issues with the current makefile thing then I prefer that

emiyl · 2026-07-24T23:38:35Z

oo right sorry i misunderstood lmao

Un1q32 · 2026-07-24T23:40:51Z

You should merge upstream cuz with the msvc 4.0 patch there was a minor change to the makefile and there might be a conflict.

Un1q32 · 2026-07-24T23:43:32Z

now the diff shows the changes from those commits. github being dumb. maybe rebase instead of merging

emiyl · 2026-07-24T23:49:00Z

#import <Cocoa/Cocoa.h>

void show_error_box(const char *message)
{
#if __has_feature(objc_arc)
    @autoreleasepool {
#else
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
#endif

        NSAlert *alert = [[NSAlert alloc] init];

        [alert setMessageText:@"Error"];
        [alert setInformativeText:[NSString stringWithUTF8String:message]];
        [alert addButtonWithTitle:@"OK"];

#if MAC_OS_X_VERSION_MAX_ALLOWED >= 101200
        [alert setAlertStyle:NSAlertStyleCritical];
#else
        [alert setAlertStyle:NSCriticalAlertStyle];
#endif

        [alert runModal];

#if !__has_feature(objc_arc)
        [alert release];
#endif

#if __has_feature(objc_arc)
    }
#else
    [pool drain];
#endif
}

This should work on OSX 10.3 and above. Before that, NSAlert doesn't exist.

Un1q32 · 2026-07-24T23:50:37Z

why have all those
#if __has_feature(objc_arc)
why not just use the non-arc path always?

emiyl · 2026-07-24T23:52:37Z

we could but if someone does compile it with arc then it'll fail 🤷 this is the most portable i could get it

Un1q32 · 2026-07-24T23:56:00Z

Also I think right now the code should in theory work on 10.0, though maybe not in practice since I think SDL 1.2 won't build. Maybe an older version of SDL 1.2 will build. Worst case just put the whole block behind a compile-time version check so it can build on 10.2 and below, though a runtime check would be nicer.

emiyl · 2026-07-24T23:57:48Z

i mean NSAlert doesn't exist on 10.0 so you'd have to use NSRunAlertPanel or something

emiyl · 2026-07-24T23:59:12Z

guess we could do

#include <AvailabilityMacros.h>

#import <AppKit/AppKit.h>

void show_error_box(const char *message)
{
#if __has_feature(objc_arc)
    @autoreleasepool {
#else
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
#endif

#if MAC_OS_X_VERSION_MAX_ALLOWED >= 1030

        NSAlert *alert = [[NSAlert alloc] init];

        [alert setMessageText:@"Error"];
        [alert setInformativeText:[NSString stringWithUTF8String:message]];
        [alert addButtonWithTitle:@"OK"];

#if MAC_OS_X_VERSION_MAX_ALLOWED >= 101200
        [alert setAlertStyle:NSAlertStyleCritical];
#else
        [alert setAlertStyle:NSCriticalAlertStyle];
#endif

        [alert runModal];

#if !__has_feature(objc_arc)
        [alert release];
#endif

#else

        NSRunAlertPanel(
            @"Error",
            [NSString stringWithUTF8String:message],
            @"OK",
            nil,
            nil
        );

#endif

#if !__has_feature(objc_arc)
    [pool drain];
#endif

#if __has_feature(objc_arc)
    }
#endif
}

Un1q32 · 2026-07-24T23:59:18Z

I need to get out my powermac again because I can't remember if the old apple compilers on 10.2 even defined the modern version macros at all. I'll prolly do that tomorrow maybe, or later today if i cant sleep.

i mean NSAlert doesn't exist on 10.0 so you'd have to use NSRunAlertPanel or something

My idea was just to do nothing and fallback to printf on stuff that can't do NSAlert, but more portability is always welcome.

emiyl · 2026-07-25T00:00:24Z

there we go - full macOS 10 compatibility lol

Un1q32 reviewed Jul 24, 2026

View reviewed changes

Comment thread src/desktop/backends/platform/macos.m Outdated

emiyl added 5 commits July 25, 2026 00:44

feat(vm): add show_error function

94eea01

add error popups for desktop frontend

debcb47

supress unused parameter warning

bcb3adc

how do brackets work again

1bbba04

specifically target darwin, and not just any apple system

3fd4ca1

emiyl added 4 commits July 25, 2026 00:44

add macos stuff to makefile

9c31449

fix makefile for macos and add .m files

73cd00a

no duplicating compiler rule

8b1661d

don't printf in the mac error box

e1376e2

emiyl force-pushed the show_error branch from 7cbd632 to e1376e2 Compare July 24, 2026 23:45

make the error message work on 10.3 and up

a845acf

macos 10.0 compatibility

c023893

emiyl added 5 commits July 25, 2026 01:03

separate into two functions

19b6569

use #include instead of #import

9f51a44

fix for devices that don't support __has_feature

dd11dc6

remove arc

fb37943

combine to one function

1afbef3

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