android opengles displaying image into texture

Question

i have rendered an image of size 480 * 800 into openGL Texture using below code, which rendered the image nicely in Samsung S3, which is of 720*1280 resolution in portrait mode.

//initialization
glEnable(GL_TEXTURE_2D);
glGenTextures(1, &s_texture);
glBindTexture(GL_TEXTURE_2D, s_texture);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); 
glShadeModel(GL_FLAT);
check_gl_error("glShadeModel");

glColor4x(0x10000, 0x10000, 0x10000, 0x10000);
check_gl_error("glColor4x");
glTexImage2D(GL_TEXTURE_2D, /* target*/
    0, /* level*/
    GL_RGBA, /* internal format*/
    480, /* width*/
    800, /* height*/
    0, /* border*/
    GL_RGBA, /* format*/
    GL_UNSIGNED_BYTE,/* type*/ //can it be GL_UNSIGNED_SHORT_5_6_5??
    0); /*source pixels*/ 
    check_gl_error("glTexImage2D");

//rendering loop
glClear(GL_COLOR_BUFFER_BIT);
glTexParameterf(GL_TEXTURE_2D,
                       GL_TEXTURE_WRAP_S,
                       GL_REPEAT);
    check_gl_error("glTexParameterf:GL_TEXTURE_WRAP_S ");
    glTexParameterf(GL_TEXTURE_2D,
                       GL_TEXTURE_WRAP_T,
                       GL_REPEAT);
    check_gl_error("glTexParameterf:GL_TEXTURE_WRAP_T");
int rect[4] = { 0, 800, 480, -800 };
    glTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_CROP_RECT_OES, rect);
glTexSubImage2D(GL_TEXTURE_2D, 0,0, 0, 480, 800, GL_RGBA, GL_UNSIGNED_BYTE, s_pixels);
check_gl_error("glTexSubImage2D");


glDrawTexiOES(0, 0, 0, screen_width, screen_height); //draw into full available window

Now i changed source image to size 720 * 1280 , Also the rendering target which is of 720*1360 resolution and is a tablet.

Now changing the above code like below doesn't seem to be working as it worked on a portrait mode device(above case). The image is not fully displayed and the partial image is repeated many times.

//initialization
glEnable(GL_TEXTURE_2D);
glGenTextures(1, &s_texture);
glBindTexture(GL_TEXTURE_2D, s_texture);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); 
glShadeModel(GL_FLAT);
check_gl_error("glShadeModel");

glColor4x(0x10000, 0x10000, 0x10000, 0x10000);
check_gl_error("glColor4x");
glTexImage2D(GL_TEXTURE_2D, /* target*/
    0, /* level*/
    GL_RGBA, /* internal format*/
    720, /* width*/
    1280, /* height*/
    0, /* border*/
    GL_RGBA, /* format*/
    GL_UNSIGNED_BYTE,/* type*/ //can it be GL_UNSIGNED_SHORT_5_6_5??
    /*s_pixels*/0); /*source pixels*/ 
    check_gl_error("glTexImage2D");

//rendering loop
glClear(GL_COLOR_BUFFER_BIT);
glTexParameterf(GL_TEXTURE_2D,
                       GL_TEXTURE_WRAP_S,
                       GL_REPEAT);
    check_gl_error("glTexParameterf:GL_TEXTURE_WRAP_S ");
    glTexParameterf(GL_TEXTURE_2D,
                       GL_TEXTURE_WRAP_T,
                       GL_REPEAT);
    check_gl_error("glTexParameterf:GL_TEXTURE_WRAP_T");
int rect[4] = { 0, 720, 1280, -720};
    glTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_CROP_RECT_OES, rect);
glTexSubImage2D(GL_TEXTURE_2D, 0,0, 0, 720, 1280, GL_RGBA, GL_UNSIGNED_BYTE, s_pixels);
check_gl_error("glTexSubImage2D");


glDrawTexiOES(0, 0, 0, screen_width, screen_height); //draw into full available window

---

1 .Can someone explain me where i do mistake ?

2 .Can someone explain me how to deal with rendering various resolution images in various dimension displays, cos all examples i saw showed that using glDrawTexiOES(0, 0, 0, screen_width, screen_height); will do it correctly, but it's not the case.

3 .If i remove int rect[4] = { 0, 720, 1280, -720}; glTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_CROP_RECT_OES, rect); i dont' see anything on screen, that's why i am using it, but i really know not the purpose of it and how to use it, can anyone tell me it's purpose and proper usage?

Answer 1

Your code looks like right, but I am not a openGL expert. Maybe that screen_width and screen_height are not right. Anyway some tips:

• It is not a good idea to create not pow to 2 textures. In some devices it will be ignored. If you want to work with a 780x1280 image, you will need to create a 1024x2048 texture. In glTexImage2D you will set "1024,2048" and in rect and glTexSubImage you will use the real image size (780x1280).
• glDrawTexiOES (and glTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_CROP_RECT_OES,) are right.
• Change GL_REPEAT to GL_CLAMP_TO_EDGE, so you will avoid that the image will get repeated.

Remember in glTexImage2D you define the texture, but the image can a part of it. In glTexSubImage and GL_TEXTURE_CROP_RECT_OES you define the part of the texture to draw, and in glDrawTexiOES you define the rect of the screen which you want to draw.