Blending

D21x，D13x 系列的显示引擎 (Display Engine) 支持一个 UI 图层和一个 Video 图层。UI 图层在 Video 图层顶部，UI 图层和 Video 图层重叠的区域进行 Color Key 操作和 Alpha 叠加操作，Color Key 操作优先于 Alpha 叠加。

Alpha Blending

UI alpha 有三种模式：pixel alpha 模式、全局 alpha 模式、混合 alpha 模式：

1、 pixels alpha 模式: ui_alpha = pixel_alpha, 当 pixel alpha 不存在时，ui_alpha = 255 2、 全局 alpha 模式: ui_alpha = G_ALPHA，G_ALPHA 为设置的全局 alpha 值，取值范围为 0~255 3、 混合 alpha 模式: ui_alpha = pixels alpha * G_ALPHA / 255

UI 图层和 Video 图层透明度混合计算：

r_out = (r_ui * alpha_ui + r_video * (255 - alpha_ui))/255
g_out = (g_ui * alpha_ui + g_video * (255 - alpha_ui))/255
b_out = (b_ui * alpha_ui + b_video * (255 - alpha_ui))/255

数据结构

#define AICFB_PIXEL_ALPHA_MODE      0
#define AICFB_GLOBAL_ALPHA_MODE     1
#define AICFB_MIXDER_ALPHA_MODE     2

/**
 * struct aicfb_alpha_config - aicfb layer alpha blending config
 *
 * @layer_id: the layer id
 *
 * @enable
 *  0: disable alpha
 *  1: enable alpha
 *
 * @mode: alpha mode
 *  0: pixel alpha mode
 *  1: global alpha mode
 *  2: mixder alpha mode(alpha = pixel alpha * global alpha / 255)
 *
 * @value: global alpha value (0~255)
 *  used by global alpha mode and mixer alpha mode
 *
 */
struct aicfb_alpha_config {
    unsigned int layer_id;
    unsigned int enable;
    unsigned int mode;
    unsigned int value;
};

/** get layer alpha blendig config */
#define AICFB_GET_ALPHA_CONFIG  _IOWR(IOC_TYPE_FB, 0x26, \
                struct aicfb_alpha_config)

/** update layer alpha blendig config */
#define AICFB_UPDATE_ALPHA_CONFIG  _IOW(IOC_TYPE_FB, 0x27, \
                struct aicfb_alpha_config)

使用例程

static int set_ui_layer_alpha(int val)
{
    int ret = 0;
    struct aicfb_alpha_config alpha = {0};

    alpha.layer_id = AICFB_LAYER_TYPE_UI;
    alpha.mode     = AICFB_GLOBAL_ALPHA_MODE;
    alpha.enable   = 1;
    alpha.value    = val;
    ret = mpp_fb_ioctl(g_mpp_fb, AICFB_UPDATE_ALPHA_CONFIG, &alpha);
    if (ret < 0)
        ERR("ioctl update alpha config failed!\n");

    return ret;
}

注解

Video 图层不支持配置 Alpha

常见问题

1、默认配置下 Video 图层不显示

Luban Lite SDK UI alpha 默认 pixel alpha 模式

pixel alpha 为 0xFF

framebuffer 缺失 alpha 分量，详见问题二

2、framebuffer RGB565/RGB888 格式设置 UI pixel alpha 模式不生效

framebuffer 16/24 bit RGB 格式缺失 pixel alpha，ui_alpha 默认为 255，UI 图层不透明，Video 图层不可见。

Color Key

通过设置 8 bit R，G，B 三原色进行 Color Key 操作

数据结构

/**
 * struct aicfb_ck_config - aicfb layer color key blending config
 *
 * @layer_id: the layer id
 *
 * @ck_enable
 *  0: disable color key
 *  1: enable color key
 *
 *
 * @ck_value: color key rgb value to match the layer pixels
 *  bit[31:24]: reserved
 *  bit[23:16]: R value
 *  bit[15:8]: G value
 *  bit[7:0]: B value
 *
 */
struct aicfb_ck_config {
    unsigned int layer_id;
    unsigned int enable;
    unsigned int value;
};

/** get layer color key config */
#define AICFB_GET_CK_CONFIG  _IOWR(IOC_TYPE_FB, 0x28, struct aicfb_ck_config)

/** update layer color key config */
#define AICFB_UPDATE_CK_CONFIG  _IOW(IOC_TYPE_FB, 0x29, struct aicfb_ck_config)

使用例程

static int set_ui_color_key(unsigned char r, unsigned char g, unsigned char b)
{
    struct aicfb_ck_config ck = {0};
    int ret = 0;
    unsigned int val;

    val = (r << 16) | (g << 8) | (b << 0);

    ck.layer_id = AICFB_LAYER_TYPE_UI;
    ck.enable   = 1;
    ck.value    = val;
    ret = mpp_fb_ioctl(g_fb_fd, AICFB_UPDATE_CK_CONFIG, &ck);
    if (ret < 0)
        printf("ioctl() failed! errno: %d[%s]\n", errno, strerror(errno));

    return ret;
}

注解

Video 图层不支持配置 Color Key

Color Key 操作在 UI 图层和 Video 图层的重叠区域进行

RGB565 Color Key

缺失的 bit 需要 循环移位 补齐，比如 G 只有 6 bit，缺失的低 2 bit 用高位来补齐：

0b101111 > 0b10111110
0b10111  > 0b10111101