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slouken/SDL3-accumulate-relative-motion.c

Created March 19, 2023 18:23
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Accumulating relative mouse motion
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SDL3-accumulate-relative-motion.c
while (SDL_PollEvent(&event) > 0) {
if (event.type == SDL_EVENT_MOUSE_MOTION) {
static float dx_frac, dy_frac;
float dx, dy;
/* Accumulate new motion with previous sub-pixel motion */
dx = event.motion.xrel + dx_frac;
dy = event.motion.yrel + dy_frac;
/* Split the integral and fractional motion, dx and dy will contain whole pixel deltas */
dx_frac = SDL_modff(dx, &dx);
dy_frac = SDL_modff(dy, &dy);
if (dx != 0.0f || dy != 0.0f) {
SDL_Log("Relative motion: %g,%g\n", dx, dy);
}
}
}
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