I using OpenGL 4.1 and GLSL 410. I am attempting to texture a square that I made using the following coordinates:
float points[] = {
-0.5, 0.5,
-0.5, -0.5,
0.5, -0.5,
-0.5, 0.5,
0.5, -0.5,
0.5, 0.5
};
I draw the square like this:
glDrawArrays (GL_TRIANGLES, 0, 6);
From all of the tutorials I have read, the author uses an element buffer to draw the square or has just four vertices. This means that all the tutorials I have read have texture coordinates that line up with each vertex. For me, I'm using 6 vertices, so I'm not sure how to line up the texture coordinates.
Would coordinates like this work for my case:
float texcoords[] = {
0.0, 1.0,
0.0, 0.0,
1.0, 0.0,
0.0, 1.0,
1.0, 0.0,
1.0, 1.0
};
I've done lots of reading, but haven't come across anyone else who is using six vertices like I am.
Would my texture coordinates work and if not, what is the best way to come up with texture coordinates.
Yes, that will work. You've divided the sqaure into 2 triangles and mapped the tex coords to the vertices of the triangles. What are your results?
See this question. The code uses one array for the vertices (although there each vertex has xyz values) and another array for the texture coords.
You need to be careful when defining the vertex attributes.
E.g. to setup the vertex data uisng 2 buffers
glGenBuffers(1, &vertexbuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(points), points, GL_STATIC_DRAW);
glGenBuffers(1, &texbuffer);
glBindBuffer(GL_ARRAY_BUFFER, texbuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(texcoords), texcoords, GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glVertexAttribPointer(0, // attribute 0
2, // 2 floats per vertex
GL_FLOAT, // type
GL_FALSE, // normalized?
0, // stride -> tightly packed so make it zero
0); // array buffer offset
glEnableVertexAttribArray(1);
glBindBuffer(GL_ARRAY_BUFFER, texbuffer);
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, NULL);
glDrawArrays(GL_TRIANGLES, 0, 6);
To load the texture (Update and setup the sampler, see comments)
glGenTextures(1, &tex);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, tex);
GLuint TextureID = glGetUniformLocation(programID, "texture");
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, x, y, 0, GL_RGBA, GL_UNSIGNED_BYTE, image_data);
Vertex shader
#version 410 core
layout (location = 0) in vec3 position;
layout (location = 1) in vec2 texcoord;
out vec2 texture_coordinates;
uniform mat4 MVP;
void main() {
gl_Position = position;
texture_coordinates = texcoord;
}
Fragment shader
in vec2 texture_coordinates;
uniform sampler2D texture;
out vec4 colour;
void main() {
colour = texture2D(basic_texture, texture_coordinates);
}
Related
I am trying to experiment and learn how to use multiple VBOs to draw very different objects in OpenGL. The first VBO is just a text renderer, and for now the shader to be used with the main VBO is just a basic vertex shader
attribute vec3 vPosition;
void main()
{
gl_Position = vec4(vPosition, 1.0);
}
Test Fragment Shader:
void main()
{
gl_FragColor = vec4(1.0, 1.0, 0.0, 1.0);
}
The code renders the text fine, but as soon as I call UseProgram and bind the VAO, I get a black screen.
Here's my initialization of said VAO:
//random polygon
points[0]= vec3(-0.5, 0.5, 0.3);
points[1]= vec3(-0.5, -0.5, 0.2);
points[2]= vec3(0.5, -0.5, 0.3);
points[3]= vec3(0.5, 0.5, 0.4);
//Returns a uInt name for a shader program
shader = InitShader("vshader.glsl", "fshader.glsl");
glGenVertexArrays(1, &vao);
glGenBuffers(1, &buffer);
glBindVertexArray(vao);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(points), points, GL_STATIC_DRAW);
GLuint loc = glGetAttribLocation(shader, "vPosition");
glEnableVertexAttribArray(loc);
glVertexAttribPointer(loc, 3, GL_FLOAT, GL_FALSE, 3*sizeof(float), BUFFER_OFFSET(0));
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);
glClearColor(1.0f, 1.0f, 1.0f, 1.0f); // white background
Where vao and buffer are previously uninitialized GLuints, and after debugging they do not return -1.
And here is my code to draw
glUseProgram(shader);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBindVertexArray(vao);
glDrawArrays(GL_POLYGON, 0, 4);
glBindVertexArray(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
Thanks for all the help everyone, I figured out that I needed to call glFlush() before binding my second VBO and VAO and drawing them.
i'm working on a project where i'm using OpenMesh to read stl and obj files and draw them on the screen using openGL.
i've been doing the following,
#include <OpenMesh/Core/Mesh/TriMesh_ArrayKernelT.hh>
#include <OpenMesh/Core/IO/MeshIO.hh>
OpenMesh::TriMesh_ArrayKernelT<> mesh;
std::vector<point> vertices;
std::vector<point> normals;
void readMesh(std::string file)
{
OpenMesh::IO::read_mesh(mesh, file);
mesh.requestFaceNormals();
mesh.request_vertex_normals();
mesh.updateNormals();
vertices.clear();
normals.clear();
for (auto face : mesh.faces())
{
for (auto vertex : mesh.fv_range(face))
{
auto point = mesh.point(vertex);
auto normal = mesh.normal(face);
vertices.push_back(point);
normals.push_back(normal);
}
}
mesh.releaseFaceNormals();
mesh.releaseVertexNormals();
}
and when drawing i just pass the vertices and normals vectors to the vertex shader like this
void paint()
{
glSetAttributeArray(0, vertices.data());
glSetAttributeArray(1, normals.data());
glDrawArrays(GL_TRIANGLES, 0, vertices.length());
}
where the vertex shader looks like this:
attribute vec3 position;
attribute vec3 normal;
uniform mat4 modelViewMatrix;
void main(void)
{
vec4 color = vec4(0.25, 0.25, 0.25, 0.0);
vec4 P = vec4(position, 0);
vec4 N = vec4(normal, 0);
vec3 L = vec3(20, 20, 20) - position;
vec3 V = -position;
N = normalize(N);
L = normalize(L);
V = normalize(V);
vec3 R = reflect(-L, vec3(N));
vec3 diffuse = max(dot(vec3(N), L), 0.0) * color.rgb;
vec3 specular = pow(max(dot(R, V), 0.0), 0.2) * vec3(0.1, 0.1, 0.1);
color = vec4(color.a * (ambient + diffuse + specular), color.a);
color = clamp(color, 0.0, 1.0);
gl_Color = color;
gl_Position = modelViewMatrix * P;
}
and the fragment shader is:
void main(void)
{
gl_FragColor = gl_Color;
}
this produces pretty good results, but the idea of having another copy of the vertices and normals stored in another location (normals and vertices) to be able to draw the mesh looks very counter-intuitive.
i was wondering if i can use openGL buffers with openMesh to optimize this. i've been searching for anything concerning this topic for a while but found nothing.
See Vertex Specification. You can create 2 Vertex Buffer Object for the verticex cooridantes and nortmal vertors:
GLuint vbos[2];
glGenBuffers(2, vbos);
glBindBuffer(GL_ARRAY_BUFFER, vbos[0]);
glBufferData(GL_ARRAY_BUFFER, vertices.size() * sizeof(vertices[0]), vertices.data(), GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, vbos[1]);
glBufferData(GL_ARRAY_BUFFER, normals.size() * sizeof(normals[0]), normals.data(), GL_STATIC_DRAW);
If you use OpenGL 3.0 or later, then you can specify a Vertex Array Object a nd state the vertex specification:
GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
glBindBuffer(GL_ARRAY_BUFFER, vbos[0]);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, nullptr);
glBindBuffer(GL_ARRAY_BUFFER, vbos[1]);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, nullptr);
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
When you want to draw the mesh, then it is sufficient to bind the VAO:
glBindVertexArray(vao);
glDrawArrays(GL_TRIANGLES, 0, vertices.length());
If you use OpenGL 2.0, the you cannot create a VAO, thus you have to specify the arrays of generic vertex attribute data, before drawing the mesh:
glBindBuffer(GL_ARRAY_BUFFER, vbos[0]);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, nullptr);
glBindBuffer(GL_ARRAY_BUFFER, vbos[1]);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, nullptr);
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
glDrawArrays(GL_TRIANGLES, 0, vertices.length());
Furthermore note, that the attribute indices are not guaranteed to be 0 and 1. The attribute indices can be any arbitrary number.
If you would use GLSL version 3.30 the it would be possible to set the attribute indices in the shader code by Layout Qualifier.
Anyway you an define the attribute indices by glBindAttribLocation before linking the program or retrieve the attribute indices by glGetAttribLocation after linking the program.
I can't get the following Code to work. I want to render the triangle I describe in position[].
The program gives me sometimes a shader compile error or a program linking error and sometimes even both without me changing the code in between.
Program:
Window window(TITLE, WIDTH, HEIGHT) // Context and glew gets init here
float position[] = {-0.5, -0.5, 0.0,
0.5, -0.5, 0.0,
0.0, 0.5, 0.0};
// Shader program gets init
sID = glCreateProgram();
vertexShaderID = glCreateShader(GL_Vertex_SHADER);
fragShaderID = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(vertexShaderID, 1, vertexShaderCodeString); // The Code strings are valid, I printed them out
glShaderSource(fragmentShaderID, 1, fragShaderCodeString);
glCompileShader(vertexShaderID);
glCompileShader(fragShaderID);
shaderDidCompileCheck(vertexShaderID); // A function I wrote that checks for errors
shaderDidCompileCheck(fragShaderID);
glAttachShader(sID, vertexShaderID);
glAttachShader(sID, fragShaderID);
glLinkProgram(sID);
programDidLinkCheck(); // A function I wrote that checks for errors
glValidateProgram(sID);
glUseProgram(sID);
glBindAttribLocation(sID, 0, "position");
glUseProgram(0);
// Defining VBOs and VAOs
int bufferID;
glGenBuffers(1, &bufferID);
glBindBuffer(GL_ARRAY_BUFFER, bufferID);
glBufferData(GL_ARRAY_BUFFER, 3 * 3 * sizeof(float), mDataPtr, GL_STATIC_DRAW); // I have 3 vertices with 3 coordinates each
glBindBuffer(GL_ARRAY_BUFFER, 0);
int vaoID;
glGenVertexArrays(1, &vaoID);
glBindVertexArray(vaoID);
glBindBuffer(GL_ARRAY_BUFFER, bufferID);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, NULL); // I Want to load it to the index 0 of the VAO, the vertex size is 3, the data type is GL_FLOAT
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);
glBindVertexArray(vaoID);
glEnableVertexAttribArray(0);
glBindVertexArray(0);
// Main loop
while(!window.close()) {
glClearColor(0.3, 0.8, 0.6, 1);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glUseProgram(sID);
glBindVertexArray(vaoID);
glDrawArrays(GL_TRIANGLES, 0, 1);
glBindVertexArray(0);
glUseProgram(0);
glfwSwapBuffers(mWindow);
glfwPollEvents();
}
Vertex Shader:
#version 410
in vec3 position;
out vec3 color;
void main() {
gl_Position = vec4(position, 1.0);
color = vec3(position.x + 0.5, 0.5, position.y + 0.5);
}
Fragment Shader:
#version 410
in vec3 color;
out vec4 outputColor;
void main() {
outputColor = vec4(color, 1.0);
}
I think there are a few typos in your code. You write "vertexShaderID = glCreateShader(GL_Vertex_SHADER)", but macros are indicated in capital letters -> "GL_VERTEX_SHADER". Try glShaderSource(vertexShaderID, 1, vertexShaderCodeString, NULL), instead of passing 3 parametrs.
How did you saved your sourcecode of the shaders ? Make shure to have \n
after the version declaration, otherwise you will end up having the code in the same line as the #, which is bad.
I'm trying to render this model in openGL:
model in image viewer
this is my attempt so far:
model rendered by my code
I only gave it the verticies so far, no normals or faces. I'm wondering why it doesn't look full like the first one. Is it because of lack of normals? I'm pretty sure I got the number of verticies/triangles right but I'm not sure if I've made mistakes. What is the next step to fully render the model like the first image?
buffer creation:
//Vertex buffer
GLuint vertexbuffer;
glGenBuffers(1, &vertexbuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);
//color buffer
GLuint colorbuffer;
glGenBuffers(1, &colorbuffer);
glBindBuffer(GL_ARRAY_BUFFER, colorbuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(g_color_buffer_data), g_color_buffer_data, GL_STATIC_DRAW);
//create shaders and attach them to a program object
GLuint program = rigShadersToProgram();
GLuint matrixID = glGetUniformLocation(program, "MVP");
rendering loop:
// Rendering loop
while (!glfwWindowShouldClose(window))
{
//clear the screen
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
////////////////////////////matrix operations/////////////////////////////////////////
//projection matrix 45 degree FoV, 4:3 ratio, display range 0.1 - 100
glm::mat4 projection = glm::perspective(99.0f, 4.0f/3.0f, 0.1f, 100.0f);
//camera matrix
glm::mat4 view = glm::lookAt(
glm::vec3(2, 1, -1), //camera is at (2,1,-1)
glm::vec3(0, 0 , 0), //looks at origin
glm::vec3(0,1, 0) //head is up
);
//model matrix identity matrix
glm::mat4 model = glm::mat4(1.0f);
//rotate
model = glm::rotate(model, e, glm::vec3(1,2,3));
//model-view-projection
glm::mat4 MVP = projection * view * model;
//////////////////////////////////////////////////////////////////////////////////////
//use the compiled shaders
glUseProgram(program);
//send transformation matrix to currently bound shader
glUniformMatrix4fv(matrixID, 1, GL_FALSE, &MVP[0][0]);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
//vertex buffer
glVertexAttribPointer(
0, //index
3, //size
GL_FLOAT, //type
GL_FALSE, //normalized?
0, //stride
0 //array buffer offset
);
glEnableVertexAttribArray(1);
glBindBuffer(GL_ARRAY_BUFFER, colorbuffer);
//color buffer
glVertexAttribPointer(
1, //index
3, //size
GL_FLOAT, //type
GL_FALSE, //normalized?
0, //stride
0 //array buffer offset
);
//draw triangle
glDrawArrays(GL_TRIANGLES, 0, 12722*3);
std::cout << glfwGetTime() << "\n";
glDisableVertexAttribArray(0);
glDisableVertexAttribArray(1);
glfwSwapBuffers(window);
glfwPollEvents();
the model data is stored in an array:
static const GLfloat g_vertex_buffer_data[] = {
-1.557376f, 0.094970f, 0.171995f,
-1.565967f, 0.098142f, 0.171995f,
-1.557376f, 0.094970f, -0.048469f,
-1.565967f, 0.098142f, -0.048469f,
-1.532660f, 0.162907f, -0.048469f,
-1.541251f, 0.166079f, -0.048469f,
-1.444236f, 0.405840f, 0.171996f,
-1.452827f, 0.409013f, 0.171996f,
-1.463533f, 0.352575f, 0.171995f,
-1.472257f, 0.355747f, 0.171995f,
-1.528166f, 0.175331f, 0.011009f,
-1.536757f, 0.178371f, 0.011009f,
-1.538475f, 0.146781f, 0.025019f, ... etc
vertex shader:
#version 430 core
layout(location =0) in vec3 vpos;
layout(location =1) in vec3 vertexColor;
out vec3 fragmentColor;
uniform mat4 MVP;
void main(void)
{
//output position of the vertex in clip space MVP*position
gl_Position = MVP * vec4(vpos,1);
fragmentColor = vertexColor;
};
fragment shader:
#version 430 core
in vec3 fragmentColor;
out vec3 color;
void main()
{
color = fragmentColor;
};
You don't show the actual model loading or rendering code. But what's clear from the screenshot of your program is, that your vertex indexing order is totally messed up. There are vertices connected with each other in your program's drawing that definitely are not connected in the model. Time to recheck the model loader code.
BTW: why did you hardcode the number of vertices to draw in the glDrawArrays call? That doesn't make sense at all.
I'm working on a rendering engine and so far it's been coming great, but I can not figure out why when I make two drawing calls to render different models, only 1 will show up.
I'm using wxWidgets to handle the window system, the code in question is pasted below. Any suggestions?
Main Rendering Loop
TestShader.Activate();
glUseProgram(TestShader.Program);
ProjectionMatrix = glm::perspective(45.0f, 4.0f / 3.0f, 0.1f, 100.0f);
int projectionMatrixLocation = glGetUniformLocation(TestShader.Program, "ProjectionMatrix");
glUniformMatrix4fv(projectionMatrixLocation, 1, GL_FALSE, glm::value_ptr(ProjectionMatrix));
glm::mat4 ViewMatrix = glm::lookAt(
glm::vec3(position),
glm::vec3(position+direction),
glm::vec3(up)
);
int viewMatrixLocation = glGetUniformLocation(TestShader.Program, "ViewMatrix");
glUniformMatrix4fv(viewMatrixLocation, 1, GL_FALSE, glm::value_ptr(ViewMatrix));
TestModel[1].Draw(TestShader, glm::vec3(0,0,-11));
TestModel[0].Draw(TestShader, glm::vec3(0,0,-1));
Refresh(false);
Model Drawing Function
void E_MODEL::Draw(EShader Shader, glm::vec3 Location)
{
if (!Registered) glGenVertexArrays(1, &VAO[0]);
glBindVertexArray(VAO[0]);
if (!Registered) glGenBuffers(1, &VBO[0]);
glBindBuffer(GL_ARRAY_BUFFER, VBO[0]);
if (!Registered) glBufferData(GL_ARRAY_BUFFER, Vertices.size() * sizeof(glm::vec3), &Vertices[0], GL_STATIC_DRAW);
if (!Registered) glGenBuffers(1, &VBO[1]);
glBindBuffer(GL_ARRAY_BUFFER, VBO[1]);
if (!Registered) glBufferData(GL_ARRAY_BUFFER, Normals.size() * sizeof(glm::vec3), &Normals[0], GL_STATIC_DRAW);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, VBO[0]);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);
glEnableVertexAttribArray(1);
glBindBuffer(GL_ARRAY_BUFFER, VBO[1]);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);
glm::mat4 modelMatrix = glm::translate(glm::mat4(1.0f), Location);
int modelMatrixLocation = glGetUniformLocation(Shader.Program, "modelMatrix");
glUniformMatrix4fv(modelMatrixLocation, 1, GL_FALSE, glm::value_ptr(modelMatrix));
glDrawArrays( GL_TRIANGLES, 0, Vertices.size() );
glDisableVertexAttribArray(0);
glDisableVertexAttribArray(1);
glBindVertexArray(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
Registered = true;
}
Vertex Shader
#version 330 core
// Input vertex data, different for all executions of this shader.
layout(location = 0) in vec3 vertexPosition_modelspace;
layout(location = 1) in vec3 vertexColor;
// Output data ; will be interpolated for each fragment.
out vec3 fragmentColor;
// Values that stay constant for the whole mesh.
uniform mat4 ProjectionMatrix;
uniform mat4 ViewMatrix;
uniform mat4 modelMatrix;
void main(){
gl_Position = ProjectionMatrix * ViewMatrix * modelMatrix * vec4(vertexPosition_modelspace,1);
// The color of each vertex will be interpolated
// to produce the color of each fragment
fragmentColor = vertexColor;
}
Fragment Shader
#version 330 core
// Interpolated values from the vertex shaders
in vec3 fragmentColor;
// Ouput data
out vec3 color;
void main(){
// Output color = color specified in the vertex shader,
// interpolated between all 3 surrounding vertices
color = fragmentColor;
}
glClear clears a buffer. With the GL_COLOR_BUFFER_BIT flag, you are clearing the color buffer. With the GL_DEPTH_BUFFER_BIT flag, you are clearing the depth buffer. By doing this each time you draw a model, the color and depth information written previously is cleared. This means you are erasing the image every time you draw a model.
You typically clear the buffers once per "paint" or "present". That is, you clear once, you draw N times, you present once. What you are doing now is clear, draw, clear, draw... present.
TL;DR: Call glClear once, before all of your drawing, not before each draw.
is it the glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); inside the draw function? maybe move that out to before you make the calls the draw functions?