How can I render RGBA4444 image in OpenGL?

March 6, 2022

I try to render my image in RGBA4444 without converting to RGBA8888,but….

// Define vertices
float vertices[] = {-1.f, 1.f,  0.f, 0.f, 1.f,   // left top
                    1.f,  1.f,  0.f, 1.f, 1.f,   // right top
                    -1.f, -1.f, 0.f, 0.f, 0.f,   // left bottom
                    1.f,  -1.f, 0.f, 1.f, 0.f};  // right bottom

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA4, image.width, image.height, 0, GL_BGRA,
             GL_UNSIGNED_SHORT_4_4_4_4_REV, image.pixels.data());

MapleStory

>Solution :

By default OpenGL assumes that the start of each row of an image is aligned to 4 bytes. This is because the GL_UNPACK_ALIGNMENT parameter by default is 4. Since a pixel of an image with the format GL_UNSIGNED_SHORT_4_4_4_4_REV only needs 2 bytes, the size of a row of the image may not be aligned to 4 bytes.
When the image is loaded to a texture object and 2*image.width is not divisible by 4, GL_UNPACK_ALIGNMENT has to be set to 2, before specifying the texture image with glTexImage2D:

glPixelStorei(GL_UNPACK_ALIGNMENT, 2);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA4, image.width, image.height, 0, GL_BGRA,
               GL_UNSIGNED_SHORT_4_4_4_4_REV, image.pixels.data());