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wayland: Pre-multiply custom cursor image alpha
Since the Wayland SHM buffer format is implicitly premultiplied and the GLFWimage pixels are defined to be non-premultiplied, we need to convert the non-premultiplied pixels to premultiplied when filling the buffer. Related to #707.
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@ -233,6 +233,13 @@ typedef VkResult (APIENTRY * PFN_vkEnumerateInstanceExtensionProperties)(const c
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y = t; \
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}
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// Helper for non-premultiplied alpha to premultiplied alpha conversion
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static inline unsigned char _glfwMultiplyAlpha(unsigned char alpha,
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unsigned char value)
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{
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return (unsigned char) ((value * (unsigned int) alpha) / 255);
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}
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//========================================================================
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// Platform-independent structures
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@ -588,10 +588,12 @@ int _glfwPlatformCreateCursor(_GLFWcursor* cursor,
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unsigned char* target = data;
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for (i = 0; i < image->width * image->height; i++, source += 4)
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{
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*target++ = source[2];
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*target++ = source[1];
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*target++ = source[0];
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*target++ = source[3];
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unsigned char alpha = source[3];
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*target++ = _glfwMultiplyAlpha(alpha, source[2]);
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*target++ = _glfwMultiplyAlpha(alpha, source[1]);
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*target++ = _glfwMultiplyAlpha(alpha, source[0]);
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*target++ = alpha;
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}
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cursor->wl.buffer =
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