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Hash : db0a2025
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Date : 2020-12-12T23:48:02
Fixed bug 5241 - SDL on Linux needs a way to turn deadzones off pj5085 It occurred to me that my simple patch that comments out a few lines of code does not correctly remove the dead zone since the calculation presumably assumes the dead zone has been cut out of the range. Then, while looking into how to make it output the correct range of values, I realized SDL wasn't returning the correct range of values to begin with. This line of code was already present: printf("Values = { %d, %d, %d, %d, %d }\n", absinfo.value, absinfo.minimum, absinfo.maximum, absinfo.fuzz, absinfo.flat); For my joystick this yeilds: Values = { 0, -127, 127, 0, 15 } Then this code calculates the coefficients: In SDL1: joystick->hwdata->abs_correct[i].coef[0] = (absinfo.maximum + absinfo.minimum) / 2 - absinfo.flat; joystick->hwdata->abs_correct[i].coef[1] = (absinfo.maximum + absinfo.minimum) / 2 + absinfo.flat; t = ((absinfo.maximum - absinfo.minimum) / 2 - 2 * absinfo.flat); if ( t != 0 ) { joystick->hwdata->abs_correct[i].coef[2] = (1 << 29) / t; } else { joystick->hwdata->abs_correct[i].coef[2] = 0; } In SDL2: joystick->hwdata->abs_correct[i].coef[0] = (absinfo.maximum + absinfo.minimum) - 2 * absinfo.flat; joystick->hwdata->abs_correct[i].coef[1] = (absinfo.maximum + absinfo.minimum) + 2 * absinfo.flat; t = ((absinfo.maximum - absinfo.minimum) - 4 * absinfo.flat); if (t != 0) { joystick->hwdata->abs_correct[i].coef[2] = (1 << 28) / t; } else { joystick->hwdata->abs_correct[i].coef[2] = 0; } Neither calculates the correct coefficients for the code in the AxisCorrect function. In SDL1: if ( value > correct->coef[0] ) { if ( value < correct->coef[1] ) { return 0; } value -= correct->coef[1]; } else { value -= correct->coef[0]; } value *= correct->coef[2]; value >>= 14; In SDL2: value *= 2; if (value > correct->coef[0]) { if (value < correct->coef[1]) { return 0; } value -= correct->coef[1]; } else { value -= correct->coef[0]; } In SDL1, the calculated coefficients are coef[0]=15, coef[1]=-15 and coef[2]=5534751. So with a full-scale input of 127, it calculates an output value of 37835, which is considerably out of range. In SDL2, the calculated coefficients are coef[0]=30, coef[1]=-30, and coef[2]=1383687. So with a full-scale input of 127, it calculates the same output value of 37835. I tested it with the 3 joysticks I have, and it produces out-of-range values for all of them. Anyway, since dead zones are garbage, I just deleted all of that junk and wrote some code that takes the absinfo.minimum and absinfo.maximum values and uses them to scale the axis range to -32767 through +32767. I also made it detect when a range doesn't have an integer center point, e.g. the center of -128 to + 127 is -0.5. In such cases, if either value to the side of the center is provided, it zeros it, but it otherwise doesn't implement any kind of dead zone. This seemed important with my gamepad which provides only the values of 0, 127, and 255, since without this hack it would never be centered. Also, the previous minimum output value was -32768, but as that creates an output range that has no true center, I changed the minimum value to -32767. I tested it with the 3 joystick devices I have and it seems to create correct values for all of them.
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Simple DirectMedia Layer (SDL) Version 2.0 --- https://www.libsdl.org/ Simple DirectMedia Layer is a cross-platform development library designed to provide low level access to audio, keyboard, mouse, joystick, and graphics hardware via OpenGL and Direct3D. It is used by video playback software, emulators, and popular games including Valve's award winning catalog and many Humble Bundle games. More extensive documentation is available in the docs directory, starting with README.md Enjoy! Sam Lantinga (slouken@libsdl.org)