Load a Cubemap

OpenGL OpenGL: Basic Coding
1

Hello :slight_smile:

I’m trying to write a program to reflect a Skybox in the objects. For this I need a cube map. But I have no Idea, how to load it.
I have also problems with loading the data of my Skybox.

I have textures to draw the Skybox, but I don’t think this will help.

Thanks for every help
Lg

2

what you need to draw the skybox:
– ability to load textures (i use SOIL, it actually has a function to create a cubemap)
– a shader, a vertexarray and a buffer (filled with cube vertices)

here is how i setup my skybox:


float vertices[] = {
		//                    vertex1            vertex2            vertex3            vertex4
		/* xpos */		+1, -1, +1,		+1, +1, +1,		+1, +1, -1,		+1, -1, -1,
		/* xneg */		-1, -1, -1,			-1, +1, -1,			-1, +1, +1,		-1, -1, +1,
		/* ypos */		-1, +1, -1,			+1, +1, -1,		+1, +1, +1,		-1, +1, +1,
		/* yneg */		-1, -1, +1,			+1, -1, +1,		+1, -1, -1,			-1, -1, -1,
		/* zpos */		+1, -1, +1,		-1, -1, +1,			-1, +1, +1,		+1, +1, +1,
		/* zneg */		-1, -1, -1,			+1, -1, -1,			+1, +1, -1,		-1, +1, -1,
	};

	// vertexarray
	glGenVertexArrays(1, &m_vao);
	glBindVertexArray(m_vao);
	
	glGenBuffers(1, &m_vbo);
	glBindBuffer(GL_ARRAY_BUFFER, m_vbo);
	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(float) * 3, (void*)(sizeof(float) * 0));
        glEnableVertexAttribArray(0);

	glBindBuffer(GL_ARRAY_BUFFER, 0);

	glBindVertexArray(0);

	// cubemap
	m_texture = SOIL_load_OGL_cubemap
	(
		"xpos.jpg",
		"xneg.jpg",
		"ypos.jpg",
		"yneg.jpg",
		"zpos.jpg",
		"zneg.jpg",
		SOIL_LOAD_RGB,
		SOIL_CREATE_NEW_ID,
		SOIL_FLAG_MIPMAPS
	);
	
	m_shader = LoadShader("skybox.vs", "skybox.fs");

here is how i render it:



	// seamless cubemap
	glEnable(GL_TEXTURE_CUBE_MAP_SEAMLESS);

	// skybox will be drawn first, so disallow writing into depth buffer
	glDepthMask(GL_FALSE);

	glUseProgram(m_shader);

	glUniformMatrix4fv(glGetUniformLocation(m_shader, "Model"), 1, false, &glm::translate(camera.Position())[0][0]);   // render cube around the view position
	glUniformMatrix4fv(glGetUniformLocation(m_shader, "View"), 1, false, &camera.View()[0][0]);	    // use instead glm::lookAt(...)
	glUniformMatrix4fv(glGetUniformLocation(m_shader, "Projection"), 1, false, &projection[0][0]);

	glUniform1i(glGetUniformLocation(m_shader, "skybox"), 0);
	glActiveTexture(GL_TEXTURE0 + 0);
	glBindTexture(GL_TEXTURE_CUBE_MAP, m_texture);

	glBindVertexArray(m_vao);
	glDrawArrays(GL_QUADS, 0, 24);
	glBindVertexArray(0);

	glBindTexture(GL_TEXTURE_CUBE_MAP, 0);
	
	glUseProgram(0);

	glDepthMask(GL_TRUE);

i render the cube (of length 1) around the viewers current position (with no rotation)
because i render the skybox first, i have to disable writing into the depth buffer
(it isnt the best solution, but it works for me ^^ it would be better to draw it after you’ve rendered the scene …)

vertexshader


#version 450

layout (location = 0) in vec3 VertexPosition;

uniform mat4 Model;
uniform mat4 View;
uniform mat4 Projection;

out vec3 TexCoords;

void main()
{
	mat4 MVP = Projection * View * Model;
	gl_Position = MVP * vec4(VertexPosition, 1.0);

    TexCoords = VertexPosition;
}

fragmentshader


#version 450

in vec3 TexCoords;

uniform samplerCube skybox;

layout (location = 0) out vec4 FragmentColor0;

void main()
{    
	FragmentColor0 = texture(skybox, TexCoords);
}
3

Thank you very much!!!
I will try to do it. You really helped me!