How to draw text on an EGL texture using Skia SkBitmap?

Question

I am looking for a way to draw text on EGLTexture using Skia library in C/C++. I am planning to run a program that does it on Android platform during bootup before SurfaceFlinge

Answer 1

I found why my code didn't work. When creating textures, the width and height must be power of 2. For example, if the width is 1920, then texture should be created with a width of 2048 (as 2048 is next 2 power).

Changed initTexture to below. Now I am able to draw text to SkBitmap and then upload the bitmap to texture and draw the texture.

Below is new initTexture that uploads given bitmap to a texture.

bool initTexture(Texture* texture, const SkBitmap &bitmap)
{
    bool result = true;
    SkAutoLockPixels alp(bitmap);

    const int w = bitmap.width();
    const int h = bitmap.height();
    const void* p = bitmap.getPixels();
    int tw = 1 << (31 - __builtin_clz(w));
    int th = 1 << (31 - __builtin_clz(h));
    if (tw < w)
        tw <<= 1;
    if (th < h)
        th <<= 1;

    if (NULL == texture)
        return false;
    if (texture->id != 0)
    {
        glBindTexture(GL_TEXTURE_2D, texture->id);
        switch (bitmap.getConfig())
        {
        case SkBitmap::kA8_Config:
            glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, w, h, GL_ALPHA, GL_UNSIGNED_BYTE, p);
            break;
        case SkBitmap::kARGB_4444_Config:
            glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, w, h, GL_RGBA, GL_UNSIGNED_SHORT_4_4_4_4, p);
            break;
        case SkBitmap::kARGB_8888_Config:
            glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, w, h, GL_RGBA, GL_UNSIGNED_BYTE, p);
            break;
        case SkBitmap::kRGB_565_Config:
            glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, w, h, GL_RGB, GL_UNSIGNED_SHORT_5_6_5, p);
            break;
        default:
            break;
        }
        return true;
    }
    GLint crop[4] = { 0, h, w, -h };
    texture->w = w;
    texture->h = h;

    glEnable (GL_TEXTURE_2D);
    glGenTextures(1, &(texture->id));
    glBindTexture(GL_TEXTURE_2D, texture->id);

    switch (bitmap.getConfig())
    {
    case SkBitmap::kA8_Config:
        glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, w, h, 0, GL_ALPHA, GL_UNSIGNED_BYTE, p);
        break;
    case SkBitmap::kARGB_4444_Config:
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, w, h, 0, GL_RGBA, GL_UNSIGNED_SHORT_4_4_4_4, p);
        break;
    case SkBitmap::kARGB_8888_Config:
        if (tw != w || th != h)
        {
            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, tw, th, 0, GL_RGBA,
                    GL_UNSIGNED_BYTE, 0);
            glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, w, h, GL_RGBA,
                    GL_UNSIGNED_BYTE, p);
        }
        else
        {
            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, w, h, 0, GL_RGBA, GL_UNSIGNED_BYTE, p);
        }
        break;
    case SkBitmap::kRGB_565_Config:
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, w, h, 0, GL_RGB, GL_UNSIGNED_SHORT_5_6_5, p);
        break;
    default:
        break;
    }

    glTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_CROP_RECT_OES, crop);
    glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    return result;
}