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| -rw-r--r-- | ppapi/c/ppb_image_data.h | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/ppapi/c/ppb_image_data.h b/ppapi/c/ppb_image_data.h index 5a7fabc..174481e 100644 --- a/ppapi/c/ppb_image_data.h +++ b/ppapi/c/ppb_image_data.h @@ -1,4 +1,4 @@ -/* Copyright (c) 2010 The Chromium Authors. All rights reserved. +/* Copyright (c) 2011 The Chromium Authors. All rights reserved. * Use of this source code is governed by a BSD-style license that can be * found in the LICENSE file. */ @@ -32,6 +32,24 @@ * the lowest address to the highest. For example, BGRA means the B component * is stored in the lowest address, no matter what endianness the platform is * using. + * + * The PREMUL suffix implies pre-multiplied alpha is used. In this mode, the + * red, green and blue color components of the pixel data supplied to an image + * data should be pre-multiplied by their alpha value. For example: starting + * with floating point color components, here is how to convert them to 8-bit + * premultiplied components for image data: + * ...components of a pixel, floats ranging from 0 to 1... + * float red = 1.0f; + * float green = 0.50f; + * float blue = 0.0f; + * float alpha = 0.75f; + * ...components for image data are 8-bit values ranging from 0 to 255... + * uint8_t image_data_red_premul = (uint8_t)(red * alpha * 255.0f); + * uint8_t image_data_green_premul = (uint8_t)(green * alpha * 255.0f); + * uint8_t image_data_blue_premul = (uint8_t)(blue * alpha * 255.0f); + * uint8_t image_data_alpha_premul = (uint8_t)(alpha * 255.0f); + * Note the resulting pre-multiplied red, green and blue components should not + * be greater than the alpha value. */ typedef enum { PP_IMAGEDATAFORMAT_BGRA_PREMUL, |