Sign in to follow this  
Shamino

OpenGL Terrain Texturing

Recommended Posts

Alright, I've been looking around for 2 days now looking at articles that are half done.. There really isn't any really good material on texturing a heightmap in opengl. I want some code snippets, not just a theory, I've read all of the theory, seen all of the procedural explainations, they stink. Can someone please attempt to walk me through texturing a terrain, with like, 1 texture? I'm not worried about two textures or more, I'm not worried about blending yet, just someone give me some insight as to how to do this.. Not a theoretical explaination! :) Please and thank you.

Share this post


Link to post
Share on other sites
I'm going to assume your map is made of quads, stored as a grid of vertices, say, a Vector3D class: grid[MAX_COLS][MAX_ROWS]
I'm also assuming that, if we're looking from the origin to your map, we're looking into the negative Z axis, with X as width, and Y as height.
For now, let's say your texture is stored at GLuint* texture

To draw a textured map, start iterating through the vertex grid




glBindTexture(GL_TEXTURE_2D, *texture); // bind the texture before you draw anything
glBegin(GL_QUADS);
for(int col = 0; col < MAX_COLS - 1; col++)
{
for(int row = 0; row < MAX_ROWS - 1; row++)
{

glTexCoord2f(1.0f, 1.0f); glVertex3f(grid[col + 1][row].x, grid[col + 1][row].y, grid[col + 1][row].z); // the top right corner
glTexCoord2f(0.0f, 1.0f); glVertex3f(grid[col][row].x, grid[col][row].y, grid[col][row].z); // the top left corner
glTexCoord2f(0.0f, 0.0f); glVertex3f(grid[col][row + 1].x, grid[col][row + 1].y, grid[col][row + 1].z); // bottom left
glTexCoord2f(1.0f, 0.0f); glVertex3f(grid[col + 1][row + 1].x, grid[col + 1][row + 1].y, grid[col + 1][row + 1].z); // bottom right


}
}
glEnd();



First off, note that you only iterate to MAX_COLS -1, because you're going to be looking 1 element away from your current position, so you do cover the entire grid.

Second, the order in which you're listing the vertices may seem weird, but listing them in counter-clockwise order makes it so OpenGL properly determines which side is GL_FRONT and which is GL_BACK

That code is basically what I'm using in my GL World terrain engine (Here) simplified a bit. Also, if you're using lighting, don't forget to specify the normals.

Share this post


Link to post
Share on other sites
Thanks alot for that lil snippet, here is my rendering code..


void RenderHeightMap(BYTE pHeightMap[]) // This Renders The Height Map As Quads
{
int X = 0, Y = 0; // Create Some Variables To Walk The Array With.
int x, y, z; // Create Some Variables For Readability

if(!pHeightMap) return; // Make Sure Our Height Data Is Valid

if(bRender) // What We Want To Render
glBegin( GL_QUADS ); // Render Polygons
else
glBegin( GL_LINES ); // Render Lines Instead

for ( X = 0; X < (MAP_SIZE-STEP_SIZE); X += STEP_SIZE )
for ( Y = 0; Y < (MAP_SIZE-STEP_SIZE); Y += STEP_SIZE )
{
// Get The (X, Y, Z) Value For The Bottom Left Vertex
x = X;
y = Height(pHeightMap, X, Y );
z = Y;

// Set The Color Value Of The Current Vertex
SetVertexColor(pHeightMap, x, z);

glVertex3i(x, y, z); // Send This Vertex To OpenGL To Be Rendered (Integer Points Are Faster)

// Get The (X, Y, Z) Value For The Top Left Vertex
x = X;
y = Height(pHeightMap, X, Y + STEP_SIZE );
z = Y + STEP_SIZE ;

// Set The Color Value Of The Current Vertex
SetVertexColor(pHeightMap, x, z);

glVertex3i(x, y, z); // Send This Vertex To OpenGL To Be Rendered

// Get The (X, Y, Z) Value For The Top Right Vertex
x = X + STEP_SIZE;
y = Height(pHeightMap, X + STEP_SIZE, Y + STEP_SIZE );
z = Y + STEP_SIZE ;

// Set The Color Value Of The Current Vertex
SetVertexColor(pHeightMap, x, z);

glVertex3i(x, y, z); // Send This Vertex To OpenGL To Be Rendered

// Get The (X, Y, Z) Value For The Bottom Right Vertex
x = X + STEP_SIZE;
y = Height(pHeightMap, X + STEP_SIZE, Y );
z = Y;

// Set The Color Value Of The Current Vertex
SetVertexColor(pHeightMap, x, z);

glVertex3i(x, y, z); // Send This Vertex To OpenGL To Be Rendered
}
glEnd();

glColor4f(1.0f, 1.0f, 1.0f, 1.0f); // Reset The Color



We are rendering the terrain with quads, I think we're already looping through each quad individually, so I'm guessing that this wouldn't be too difficult to implement what you just gave me in this bit of code, I'll give it a shot.

Share this post


Link to post
Share on other sites
If you know how to stretch a texture across a quad, then it is relatively straightforward to stretch it across a mesh. Both simply assign texture coordinates in the range 0.0 to 1.0 to the vertices. Two corners opposite each other in the single quad will have (0.0,0.0) and (1.0,1.0) respectively. The same thing with the terrain mesh. All of the vertices inbetween are in between 0.0 and 1.0.

Eg, the single quad would look something like this for the U and V texture coordinates


(0.0,1.0)-----(1.0,1.0)
| |
| |
| |
| |
| |
| |
(0.0,0.0)-----(1.0,0.0)


For a 5x5 mesh it would look like this:

0 1 2 3 4
0 (0.00,1.00)-----(0.25,1.00)-----(0.50,1.00)-----(0.75,1.00)-----(1.00,1.00)
| | | | |
| | | | |
| | | | |
| | | | |
| | | | |
| | | | |
1 (0.00,0.75)-----(0.25,0.75)-----(0.50,0.75)-----(0.75,0.75)-----(1.00,0.75)
| | | | |
| | | | |
| | | | |
| | | | |
| | | | |
| | | | |
2 (0.00,0.50)-----(0.25,0.50)-----(0.50,0.50)-----(0.75,0.50)-----(1.00,0.50)
| | | | |
| | | | |
| | | | |
| | | | |
| | | | |
| | | | |
3 (0.00,0.25)-----(0.25,0.25)-----(0.50,0.25)-----(0.75,0.25)-----(1.00,0.25)
| | | | |
| | | | |
| | | | |
| | | | |
| | | | |
| | | | |
4 (0.00,0.00)-----(0.25,0.00)-----(0.50,0.00)-----(0.75,0.00)-----(1.00,0.00)


So your render routine simply need to calculate the appropriate texture coordinate for the vertex it is currently processes. I do it like this:



terrain.size = 5;

// texture corrdinate variables
float a,b,c;

// render heightmap mesh
for ( int row = 0; row < (terrain.size-1); row++ ) { // X axis

// draw triangle strip
glBegin(GL_TRIANGLE_STRIP);

for ( int col = 0; col < terrain.size; col++ ) { // Z axis

// caclulate texture coordinates for this vertex
a = (float)row/(terrain.size-1);
b = (float)col/(terrain.size-1);
c = (float)(row+1)/(terrain.size-1);

// set first vertex normal
glNormal3f(terrain.CNormal[row][col].x,terrain.CNormal[row][col].y,terrain.CNormal[row][col].z);

// set texture coordinates for first vertex
if ( terrain.textureMode ) {
glMultiTexCoord2fARB( GL_TEXTURE0_ARB, a, b );
glMultiTexCoord2fARB( GL_TEXTURE1_ARB, a*terrain.detailRepeat, b*terrain.detailRepeat);
}

// draw first vertex
glVertex3f( (terrain.CPoint[row][col].x+terrain.step)*terrain.scale,
(terrain.CPoint[row][col].y+terrain.step)*terrain.scale,
(terrain.CPoint[row][col].z+terrain.step)*terrain.scale);

// set second vertex normal
glNormal3f(terrain.CNormal[row+1][col].x,terrain.CNormal[row+1][col].y,terrain.CNormal[row+1][col].z);

// set second vertex texture coordinates
if ( terrain.textureMode ) {
glMultiTexCoord2fARB( GL_TEXTURE0_ARB, c, b );
glMultiTexCoord2fARB( GL_TEXTURE1_ARB, c*terrain.detailRepeat, b*terrain.detailRepeat );
}

// draw second vertex
glVertex3f( (terrain.CPoint[row+1][col].x+terrain.step)*terrain.scale,
(terrain.CPoint[row+1][col].y+terrain.step)*terrain.scale,
(terrain.CPoint[row+1][col].z+terrain.step)*terrain.scale);
}

glEnd();
}




I use a triangle strip since they require less vertices to render. If you wanted to repeat the same texture for each quad, then you would simply use the coordinates for the single quad.

hth
F451

Share this post


Link to post
Share on other sites
I thought no matter what the tex coords were always

(1.0, 1.0) - Top Right
(0.0, 1.0) - Top Left
(0.0, 0.0) - Bottom Left
(1.0, 0.0) - Bottom Right

So no matter what the vertices we're working with are, we just need to know which one is the top right, top left, bottom left, and bottom right, then we can just set the tex coords accordingly..

For the top right vertice, we just do this...

Oh wait I just saw you said if you want to repeat a texture just repeat the coords for each quad...

That's what I'm gonna do :)

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Announcements

  • Forum Statistics

    • Total Topics
      628308
    • Total Posts
      2981974
  • Similar Content

    • By mellinoe
      Hi all,
      First time poster here, although I've been reading posts here for quite a while. This place has been invaluable for learning graphics programming -- thanks for a great resource!
      Right now, I'm working on a graphics abstraction layer for .NET which supports D3D11, Vulkan, and OpenGL at the moment. I have implemented most of my planned features already, and things are working well. Some remaining features that I am planning are Compute Shaders, and some flavor of read-write shader resources. At the moment, my shaders can just get simple read-only access to a uniform (or constant) buffer, a texture, or a sampler. Unfortunately, I'm having a tough time grasping the distinctions between all of the different kinds of read-write resources that are available. In D3D alone, there seem to be 5 or 6 different kinds of resources with similar but different characteristics. On top of that, I get the impression that some of them are more or less "obsoleted" by the newer kinds, and don't have much of a place in modern code. There seem to be a few pivots:
      The data source/destination (buffer or texture) Read-write or read-only Structured or unstructured (?) Ordered vs unordered (?) These are just my observations based on a lot of MSDN and OpenGL doc reading. For my library, I'm not interested in exposing every possibility to the user -- just trying to find a good "middle-ground" that can be represented cleanly across API's which is good enough for common scenarios.
      Can anyone give a sort of "overview" of the different options, and perhaps compare/contrast the concepts between Direct3D, OpenGL, and Vulkan? I'd also be very interested in hearing how other folks have abstracted these concepts in their libraries.
    • By aejt
      I recently started getting into graphics programming (2nd try, first try was many years ago) and I'm working on a 3d rendering engine which I hope to be able to make a 3D game with sooner or later. I have plenty of C++ experience, but not a lot when it comes to graphics, and while it's definitely going much better this time, I'm having trouble figuring out how assets are usually handled by engines.
      I'm not having trouble with handling the GPU resources, but more so with how the resources should be defined and used in the system (materials, models, etc).
      This is my plan now, I've implemented most of it except for the XML parts and factories and those are the ones I'm not sure of at all:
      I have these classes:
      For GPU resources:
      Geometry: holds and manages everything needed to render a geometry: VAO, VBO, EBO. Texture: holds and manages a texture which is loaded into the GPU. Shader: holds and manages a shader which is loaded into the GPU. For assets relying on GPU resources:
      Material: holds a shader resource, multiple texture resources, as well as uniform settings. Mesh: holds a geometry and a material. Model: holds multiple meshes, possibly in a tree structure to more easily support skinning later on? For handling GPU resources:
      ResourceCache<T>: T can be any resource loaded into the GPU. It owns these resources and only hands out handles to them on request (currently string identifiers are used when requesting handles, but all resources are stored in a vector and each handle only contains resource's index in that vector) Resource<T>: The handles given out from ResourceCache. The handles are reference counted and to get the underlying resource you simply deference like with pointers (*handle).  
      And my plan is to define everything into these XML documents to abstract away files:
      Resources.xml for ref-counted GPU resources (geometry, shaders, textures) Resources are assigned names/ids and resource files, and possibly some attributes (what vertex attributes does this geometry have? what vertex attributes does this shader expect? what uniforms does this shader use? and so on) Are reference counted using ResourceCache<T> Assets.xml for assets using the GPU resources (materials, meshes, models) Assets are not reference counted, but they hold handles to ref-counted resources. References the resources defined in Resources.xml by names/ids. The XMLs are loaded into some structure in memory which is then used for loading the resources/assets using factory classes:
      Factory classes for resources:
      For example, a texture factory could contain the texture definitions from the XML containing data about textures in the game, as well as a cache containing all loaded textures. This means it has mappings from each name/id to a file and when asked to load a texture with a name/id, it can look up its path and use a "BinaryLoader" to either load the file and create the resource directly, or asynchronously load the file's data into a queue which then can be read from later to create the resources synchronously in the GL context. These factories only return handles.
      Factory classes for assets:
      Much like for resources, these classes contain the definitions for the assets they can load. For example, with the definition the MaterialFactory will know which shader, textures and possibly uniform a certain material has, and with the help of TextureFactory and ShaderFactory, it can retrieve handles to the resources it needs (Shader + Textures), setup itself from XML data (uniform values), and return a created instance of requested material. These factories return actual instances, not handles (but the instances contain handles).
       
       
      Is this a good or commonly used approach? Is this going to bite me in the ass later on? Are there other more preferable approaches? Is this outside of the scope of a 3d renderer and should be on the engine side? I'd love to receive and kind of advice or suggestions!
      Thanks!
    • By nedondev
      I 'm learning how to create game by using opengl with c/c++ coding, so here is my fist game. In video description also have game contain in Dropbox. May be I will make it better in future.
      Thanks.
    • By Abecederia
      So I've recently started learning some GLSL and now I'm toying with a POM shader. I'm trying to optimize it and notice that it starts having issues at high texture sizes, especially with self-shadowing.
      Now I know POM is expensive either way, but would pulling the heightmap out of the normalmap alpha channel and in it's own 8bit texture make doing all those dozens of texture fetches more cheap? Or is everything in the cache aligned to 32bit anyway? I haven't implemented texture compression yet, I think that would help? But regardless, should there be a performance boost from decoupling the heightmap? I could also keep it in a lower resolution than the normalmap if that would improve performance.
      Any help is much appreciated, please keep in mind I'm somewhat of a newbie. Thanks!
    • By test opty
      Hi,
      I'm trying to learn OpenGL through a website and have proceeded until this page of it. The output is a simple triangle. The problem is the complexity.
      I have read that page several times and tried to analyse the code but I haven't understood the code properly and completely yet. This is the code:
       
      #include <glad/glad.h> #include <GLFW/glfw3.h> #include <C:\Users\Abbasi\Desktop\std_lib_facilities_4.h> using namespace std; //****************************************************************************** void framebuffer_size_callback(GLFWwindow* window, int width, int height); void processInput(GLFWwindow *window); // settings const unsigned int SCR_WIDTH = 800; const unsigned int SCR_HEIGHT = 600; const char *vertexShaderSource = "#version 330 core\n" "layout (location = 0) in vec3 aPos;\n" "void main()\n" "{\n" " gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n" "}\0"; const char *fragmentShaderSource = "#version 330 core\n" "out vec4 FragColor;\n" "void main()\n" "{\n" " FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n" "}\n\0"; //******************************* int main() { // glfw: initialize and configure // ------------------------------ glfwInit(); glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3); glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); // glfw window creation GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "My First Triangle", nullptr, nullptr); if (window == nullptr) { cout << "Failed to create GLFW window" << endl; glfwTerminate(); return -1; } glfwMakeContextCurrent(window); glfwSetFramebufferSizeCallback(window, framebuffer_size_callback); // glad: load all OpenGL function pointers if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) { cout << "Failed to initialize GLAD" << endl; return -1; } // build and compile our shader program // vertex shader int vertexShader = glCreateShader(GL_VERTEX_SHADER); glShaderSource(vertexShader, 1, &vertexShaderSource, nullptr); glCompileShader(vertexShader); // check for shader compile errors int success; char infoLog[512]; glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success); if (!success) { glGetShaderInfoLog(vertexShader, 512, nullptr, infoLog); cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << endl; } // fragment shader int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER); glShaderSource(fragmentShader, 1, &fragmentShaderSource, nullptr); glCompileShader(fragmentShader); // check for shader compile errors glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success); if (!success) { glGetShaderInfoLog(fragmentShader, 512, nullptr, infoLog); cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << endl; } // link shaders int shaderProgram = glCreateProgram(); glAttachShader(shaderProgram, vertexShader); glAttachShader(shaderProgram, fragmentShader); glLinkProgram(shaderProgram); // check for linking errors glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success); if (!success) { glGetProgramInfoLog(shaderProgram, 512, nullptr, infoLog); cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << endl; } glDeleteShader(vertexShader); glDeleteShader(fragmentShader); // set up vertex data (and buffer(s)) and configure vertex attributes float vertices[] = { -0.5f, -0.5f, 0.0f, // left 0.5f, -0.5f, 0.0f, // right 0.0f, 0.5f, 0.0f // top }; unsigned int VBO, VAO; glGenVertexArrays(1, &VAO); glGenBuffers(1, &VBO); // bind the Vertex Array Object first, then bind and set vertex buffer(s), //and then configure vertex attributes(s). glBindVertexArray(VAO); glBindBuffer(GL_ARRAY_BUFFER, VBO); glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW); glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0); glEnableVertexAttribArray(0); // note that this is allowed, the call to glVertexAttribPointer registered VBO // as the vertex attribute's bound vertex buffer object so afterwards we can safely unbind glBindBuffer(GL_ARRAY_BUFFER, 0); // You can unbind the VAO afterwards so other VAO calls won't accidentally // modify this VAO, but this rarely happens. Modifying other // VAOs requires a call to glBindVertexArray anyways so we generally don't unbind // VAOs (nor VBOs) when it's not directly necessary. glBindVertexArray(0); // uncomment this call to draw in wireframe polygons. //glPolygonMode(GL_FRONT_AND_BACK, GL_LINE); // render loop while (!glfwWindowShouldClose(window)) { // input // ----- processInput(window); // render // ------ glClearColor(0.2f, 0.3f, 0.3f, 1.0f); glClear(GL_COLOR_BUFFER_BIT); // draw our first triangle glUseProgram(shaderProgram); glBindVertexArray(VAO); // seeing as we only have a single VAO there's no need to // bind it every time, but we'll do so to keep things a bit more organized glDrawArrays(GL_TRIANGLES, 0, 3); // glBindVertexArray(0); // no need to unbind it every time // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.) glfwSwapBuffers(window); glfwPollEvents(); } // optional: de-allocate all resources once they've outlived their purpose: glDeleteVertexArrays(1, &VAO); glDeleteBuffers(1, &VBO); // glfw: terminate, clearing all previously allocated GLFW resources. glfwTerminate(); return 0; } //************************************************** // process all input: query GLFW whether relevant keys are pressed/released // this frame and react accordingly void processInput(GLFWwindow *window) { if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS) glfwSetWindowShouldClose(window, true); } //******************************************************************** // glfw: whenever the window size changed (by OS or user resize) this callback function executes void framebuffer_size_callback(GLFWwindow* window, int width, int height) { // make sure the viewport matches the new window dimensions; note that width and // height will be significantly larger than specified on retina displays. glViewport(0, 0, width, height); } As you see, about 200 lines of complicated code only for a simple triangle. 
      I don't know what parts are necessary for that output. And also, what the correct order of instructions for such an output or programs is, generally. That start point is too complex for a beginner of OpenGL like me and I don't know how to make the issue solved. What are your ideas please? What is the way to figure both the code and the whole program out correctly please?
      I wish I'd read a reference that would teach me OpenGL through a step-by-step method. 
  • Popular Now