在Emscripten中使用SDL2 RenderDraw函数 [英] Using SDL2 RenderDraw functions with Emscripten
问题描述
我一直在努力将使用SDL2图形的简单C程序通过emscripten移植到Web.我浏览了示例程序,但找不到使用SDL_RenderDrawPoint,SDL_RenderDrawLine或SDL_RenderDrawRect绘制到屏幕上的程序.这些功能在我的程序的Windows/ubuntu版本上有效,但在emscripten版本上无效.我只是看到屏幕上涂有清除的颜色,但没有画任何东西.
I've been struggling to port a simple C program that uses SDL2 for graphics to the web using emscripten. I scanned through example programs but was unable to find one that draws to the screen using SDL_RenderDrawPoint, SDL_RenderDrawLine, or SDL_RenderDrawRect. These functions work on the windows/ubuntu versions of my program, but not on the emscripten version. I simply see the screen painted with the cleared color, but nothing drawn to it.
这里是展示问题的示例代码.
Here's sample code that showcases the issue.
#include <stdio.h>
#include <SDL2/SDL.h>
#include <assert.h>
#ifdef __EMSCRIPTEN__
#include <emscripten.h>
#endif
int main(int argc, char* argv[])
{
// setup
SDL_Window * window;
SDL_Renderer * renderer;
assert(SDL_Init(SDL_INIT_VIDEO) == 0);
SDL_CreateWindowAndRenderer(640, 320, 0, &window, &renderer);
// clear screen with red color
SDL_SetRenderDrawColor(renderer, 200, 0, 0, 255);
SDL_RenderClear(renderer);
// draw green line across screen
SDL_SetRenderDrawColor(renderer, 0, 255, 0, 255);
SDL_RenderDrawLine(renderer, 0, 0, 640, 320);
SDL_RenderPresent(renderer);
SDL_Delay(2000);
// free resources
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
return 0;
}
我将此代码保存到main.c中,然后运行:
I saved this code to main.c then ran:
emcc main.c -s USE_SDL = 2 -o a.html
在Windows/Ubuntu上,我看到以下内容:
On Windows/Ubuntu, I see this:
在Emscripten(Chrome)上,我看到以下内容:
On Emscripten (Chrome) I see this:
这是一个错误,还是我做错了什么?
Is this a bug, or am I doing something wrong?
推荐答案
使用emscripten,您几乎总是必须使用其主循环方法.使用 SDL_Delay
或任何其他形式的睡眠都是不好的,因为它与普通PC目标的工作方式不同(更像是自旋锁而不是睡眠).您应该使用类似这样的内容:
With emscripten you almost always have to use its main loop approach. Using SDL_Delay
or any other form of sleeping is bad because it works differently from ordinary PC targets (more like spinlock than sleep). You should use something like:
#include <stdio.h>
#include <SDL2/SDL.h>
#include <assert.h>
#ifdef __EMSCRIPTEN__
#include <emscripten.h>
#endif
SDL_Window * window;
SDL_Renderer * renderer;
void render_func(void) {
SDL_SetRenderDrawColor(renderer, 200, 0, 0, 255);
SDL_RenderClear(renderer);
SDL_SetRenderDrawColor(renderer, 0, 255, 0, 255);
SDL_RenderDrawLine(renderer, 0, 0, 640, 320);
SDL_RenderPresent(renderer);
#ifdef EMSCRIPTEN
emscripten_cancel_main_loop();
#endif
}
int main(int argc, char* argv[])
{
assert(SDL_Init(SDL_INIT_VIDEO) == 0);
SDL_CreateWindowAndRenderer(640, 320, 0, &window, &renderer);
#ifdef EMSCRIPTEN
emscripten_set_main_loop(render_func, 60, 1);
#else
render_func();
#endif
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
return 0;
}
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