Where did you get your asteroid model?
I was following the Learn OpenGL tutorials and got the model and information on how to do modern Skyboxes from him. Though I understood how they work, I just didn't understand modern techniques, which have improved. Also see his section on instancing which is where I learned this. He has a link to this asteroid model, though you can use any model you wish once you get the model loading code down pat. A direct link to it is here (from his website)...
https://learnopengl.com/Advanced-OpenGL/data/models/rock.rar
Quote:
I still don't understand what happens when you look at the corners of the skybox. Shouldn't the textures be totally distorted?
If you had a normal field of view, they absolutely would be distorted. But when you create a skybox, you render each view with a 90 degree field of view (as opposed to your normal 45-60 degree FOV most games use). You have four sides plus the top and bottom. In order to get a perfect 360 degree panaramic view, you need to have each of the four sides (plus top and bottom) be 360/4=90 degrees. So once you combine them all, you get what appears to be a panaramic, perfect 360 view you can look around and no corners. The 90 degree FOV textures actually look a little distorted until you put them on the inside of a cube for the skybox.
Now if you JUST make a cube with the 90 degree FOV textures, you will see the corners. You need to turn off lighting which will shade the sides and show shadows in the corners and just light the entire texture evenly by setting a colour as I did as pure white to light up the entire texture. You also turn off things like fog etc when you render the skybox. You clamp the edges (see my previous older code which contains code for clamping that is still valid), what that does is it ensure the texture goes all the way to the edge so no seams are visible between textures.
What you see when you see a corner is shadowing, lighting etc... plus if your textures are views which are less than 90 degree FOV, than you notice it. Think about it, if you try and fit a 45 degree FOV image onto a side which is a 90 degree FOV, you will get distortion unless the view was 90 degrees ahead of time.
Also, check out the Java tutorial Chris posted above, it explains modern skyboxes very nicely. Even though it is Java, it translates over to C/C++ easily. But the concepts are the same.
Quote:
Neil, could you show me where you setup your projection matrices for the skybox?
Learn OpenGL does a great job explaining this and even provides code if you get stuck. This is the modern method which is more involved, but well worth it.
https://learnopengl.com/Advanced-OpenGL/Cubemaps
If you followed along with these tutorials, I basically just needed to insert this code (though I had to alter some of it as he had errors in it, easy fix)...
#SelectExpand
1Shader skyboxShader("6.1.skybox.vs", "6.1.skybox.fs");
2
3 float skyboxVertices[] = {
4 // positions
5 -1.0f, 1.0f, -1.0f,
6 -1.0f, -1.0f, -1.0f,
7 1.0f, -1.0f, -1.0f,
8 1.0f, -1.0f, -1.0f,
9 1.0f, 1.0f, -1.0f,
10 -1.0f, 1.0f, -1.0f,
11
12 -1.0f, -1.0f, 1.0f,
13 -1.0f, -1.0f, -1.0f,
14 -1.0f, 1.0f, -1.0f,
15 -1.0f, 1.0f, -1.0f,
16 -1.0f, 1.0f, 1.0f,
17 -1.0f, -1.0f, 1.0f,
18
19 1.0f, -1.0f, -1.0f,
20 1.0f, -1.0f, 1.0f,
21 1.0f, 1.0f, 1.0f,
22 1.0f, 1.0f, 1.0f,
23 1.0f, 1.0f, -1.0f,
24 1.0f, -1.0f, -1.0f,
25
26 -1.0f, -1.0f, 1.0f,
27 -1.0f, 1.0f, 1.0f,
28 1.0f, 1.0f, 1.0f,
29 1.0f, 1.0f, 1.0f,
30 1.0f, -1.0f, 1.0f,
31 -1.0f, -1.0f, 1.0f,
32
33 -1.0f, 1.0f, -1.0f,
34 1.0f, 1.0f, -1.0f,
35 1.0f, 1.0f, 1.0f,
36 1.0f, 1.0f, 1.0f,
37 -1.0f, 1.0f, 1.0f,
38 -1.0f, 1.0f, -1.0f,
39
40 -1.0f, -1.0f, -1.0f,
41 -1.0f, -1.0f, 1.0f,
42 1.0f, -1.0f, -1.0f,
43 1.0f, -1.0f, -1.0f,
44 -1.0f, -1.0f, 1.0f,
45 1.0f, -1.0f, 1.0f
46 };
47
48 // skybox VAO
49 unsigned int skyboxVAO, skyboxVBO;
50 glGenVertexArrays(1, &skyboxVAO);
51 glGenBuffers(1, &skyboxVBO);
52 glBindVertexArray(skyboxVAO);
53 glBindBuffer(GL_ARRAY_BUFFER, skyboxVBO);
54 glBufferData(GL_ARRAY_BUFFER, sizeof(skyboxVertices), &skyboxVertices, GL_STATIC_DRAW);
55 glEnableVertexAttribArray(0);
56 glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
57
58 // Skybox Textures
59 vector<std::string> faces
60 {
61 "resources/textures/skybox/space_right.jpg",
62 "resources/textures/skybox/space_left.jpg",
63 "resources/textures/skybox/space_top.jpg",
64 "resources/textures/skybox/space_bottom.jpg",
65 "resources/textures/skybox/space_front.jpg",
66 "resources/textures/skybox/space_back.jpg"
67 };
68 unsigned int cubemapTexture = loadCubemap(faces);
69
70 skyboxShader.use();
71 skyboxShader.setInt("skybox", 0);
I of course created my own space skybox textures and re-organized their loading order as his was flawed. See his tutorials for other functions mentioned here.
Now for drawing the skybox, he had some great optimizations. Normally, using the old OPenGL (see my code again above) you would disable depth testing and draw the skybox first (back to front). But in this newer code, you actually leave depth testing on and draw the skybox last, which one might think would overwrite the foreground objects, but what you do is adjust settings for the depth testing so that it only draws the parts of the skybox that are visible without overwriting foreground objects. As a result, this makes it FASTER to render it as you can skip over entire fragments which are not visible. Kewl beans! 
// draw skybox as last
glDepthFunc(GL_LEQUAL); // change depth function so depth test passes when values are equal to depth buffer's content
skyboxShader.use();
view = glm::mat4(glm::mat3(camera.GetViewMatrix())); // remove translation from the view matrix
skyboxShader.setMat4("view", view);
skyboxShader.setMat4("projection", projection);
// skybox cube
glBindVertexArray(skyboxVAO);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_CUBE_MAP, cubemapTexture);
glDrawArrays(GL_TRIANGLES, 0, 36);
glBindVertexArray(0);
glDepthFunc(GL_LESS); // set depth function back to default
There are separate shader programs you use for the asteroids. The fragment shaders (which are loaded and compiled when you run the game then sent to the video card).
Fragment shader for asteroids...
#version 330 core
out vec4 FragColor;
in vec2 TexCoords;
uniform sampler2D texture_diffuse1;
void main()
{
FragColor = texture(texture_diffuse1, TexCoords);
}
Vertex shader for asteroids...
#SelectExpand
1#version 330 core
2layout (location = 0) in vec3 aPos;
3layout (location = 2) in vec2 aTexCoords;
4layout (location = 3) in mat4 aInstanceMatrix;
5
6out vec2 TexCoords;
7
8uniform mat4 projection;
9uniform mat4 view;
10
11void main()
12{
13 TexCoords = aTexCoords;
14 gl_Position = projection * view * aInstanceMatrix * vec4(aPos, 1.0f);
15}
It really is well worth just following along those tutorials, in order and you will understand all of this. They're very well explained, probably the best on the net that I have seen.
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