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I am trying to use sprite sheet in OpenGL, implementing it through Array Texture
This is how I load my texture:

QImage image;
image.load("C:\\QtProjects\\project\\images\\spritesheet.png", "png");
const unsigned char* data = image.bits();
int twidth = image.width(), theight = image.height();
glTexStorage3D(GL_TEXTURE_2D_ARRAY, 1, GL_RGBA, twidth / 3, theight / 4, 12);
glTexSubImage3D(GL_TEXTURE_2D_ARRAY, 0, 0, 0, 0, twidth / 3, theight / 4, 12, GL_BGRA, GL_UNSIGNED_BYTE, data);
glUseProgram(scene_program);

glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

This is my fragment shader:

#version 330 core

in vec3 Color;
in vec2 Texture_coord;

out vec4 outColor;

uniform sampler2DArray tex;

void main()
{
    vec2 coord;
    coord.x = Texture_coord.x;
    coord.y = Texture_coord.y;

    vec4 color = texture(tex, vec3(coord, 0));

    outColor = color;
}

I am drawing it to the quad with texture coordinates (0.0, 0.0) in one corner and (1.0, 1.0) in other, so I expect to get a first sprite from first row on my quad.
But I get this corrupted piece of image: https://i.sstatic.net/bfXgr.jpg
This is whole sprite sheet: https://i.sstatic.net/LaZKP.png

P.S.: whole image is loaded correctly, I can display it or it's part through traditional GL_TEXTURE_2D

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  • Why aren't you using QOpenGLTexture, QOpenGLShaderProgram, QOpenGLDebugLogger etc.? From the few lines of code you've pasted it looks like your texture might be mipmap-incomplete. Commented Aug 17, 2014 at 15:05
  • @peppe, thanks for the answer. Oh, it's funny :D I don't use all of these because I don't know about these. I will try, may be my problem can be fixed Also I was not interested in this because I wanted to learn pure OpenGL Commented Aug 17, 2014 at 15:23

1 Answer 1

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I don't believe the problem is directly related to array textures. The real issue is in how you are trying to load part of your input image into a texture:

glTexStorage3D(GL_TEXTURE_2D_ARRAY, 1, GL_RGBA, twidth / 3, theight / 4, 12);
glTexSubImage3D(GL_TEXTURE_2D_ARRAY, 0, 0, 0, 0, twidth / 3, theight / 4, 12,
                GL_BGRA, GL_UNSIGNED_BYTE, data);

The glTexSubImage3D() call does not know how large your input image is. it will simply read your image data sequentially based on the sizes you pass in as parameters. If you give it width that is 1/3 of your original image width, it will read 3 texture rows from the first row of your input image, then another 3 texture rows from the second row of your image, etc.

You can specify the size of your input rows (in pixels) with the GL_UNPACK_ROW_LENGTH pixel storage value. For your case, the following call specifies the width of your input image:

glPixelStorei(GL_UNPACK_ROW_LENGTH, twidth);

I don't think there's a reasonable way of loading your whole sprite sheet into the array texture with a single glTexSubImage3D() call. It's probably easiest if you make a separate call for each image. The whole thing will then look like this:

GLuint texId = 0;
glGenTextures(1, &texId);

glBindTexture(GL_TEXTURE_2D_ARRAY, texId);

glTexParameteri(GL_TEXTURE_2D_ARRAY, ...);

int subWidth = twidth / 3;
int subHeight = theight / 4;

glTexStorage3D(GL_TEXTURE_2D_ARRAY, 1, GL_RGBA, subWidth, subHeight, 12);

glPixelStorei(GL_UNPACK_ROW_LENGTH, twidth);

for (int iRow = 0; iRow < 4; ++iRow) {
    for (int iCol = 0; iCol < 3; ++iCol) {
        glTexSubImage3D(
            GL_TEXTURE_2D_ARRAY, 0,
            0, 0, 3 * iRow + iCol,
            subWidth, subHeight, 1,
            GL_BGRA, GL_UNSIGNED_BYTE,
            data + (iRow * subHeight * twidth + iCol * subWidth) * 4);
    }
}

You could try to avoid the separate calls by using other unpack parameters like GL_UNPACK_IMAGE_HEIGHT, but I'm not convinced that there are settings that would work for this case.

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7 Comments

Thanks. May be I misunderstood a part of conception. I give arguments twidth / 3, theight / 4 because I think that I must give width and height of 1 (one) image from the sprite sheet (while all others have same size). Am I wrong? Hmm, why it is better to load sprites separately?
The arguments give the size of the texture you create. If you don't set GL_UNPACK_ROW_LENGTH, it will assume that the input image has the same size. But the width of your input image is twidth, not twidth / 3.
Please, could you show me, how the whole piece of code looks like? (from glTexStorage3D to last glTexSubImage3D) I've tried all your tips in different combinations, but nothing works (even separate loading: each glTexSubImage3D call gives GL_INVALID_OPERATION, I read manpage and I can't understand which reason for this error is in my case). I am missing something
Hey? Can you please help me?
I just tried the code I posted, and it works fine for me. I edited the answer to put all the pieces in sequence.
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