Ways to debug glDrawElements in OpenGL ES - opengl-es

I have a set of vertices and indices
static const GLfloat cubeVertices[192] = {
// right 0
0.5f, -0.5f, -0.5f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f,
.....
};
unsigned int cubeIndices[36] = {
// right
0, 1, 2, 2, 3, 0,
....
};
Full Data Here: http://stevezissouprogramming.blogspot.com/2012/03/basic-cube-part-3-drawing.html
// Create the Vertex Buffer
glGenBuffers(1, &_vertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(cubeVertices), cubeVertices, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
// Create the Indices Buffer
glGenBuffers(1, &_indicesBuffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _indicesBuffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(cubeIndices), cubeIndices, GL_STATIC_DRAW);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
// tell openGL how to interpret the buffers
GLsizei stride = sizeof(GLfloat) * 8; // 8 components per row = 4 * 8 = 32
glEnableVertexAttribArray(GLKVertexAttribPosition);
glEnableVertexAttribArray(GLKVertexAttribNormal);
glEnableVertexAttribArray(GLKVertexAttribTexCoord0);
glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, stride, BUFFER_OFFSET(0));
glVertexAttribPointer(GLKVertexAttribNormal, 3, GL_FLOAT, GL_FALSE, stride, BUFFER_OFFSET(stride*3/8));
glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, stride, BUFFER_OFFSET(stride*6/8));
and then in my draw method I have
glDrawElements(GL_TRIANGLES, 24, GL_UNSIGNED_INT, NULL);
I first created the example using only the vertices array and glDrawArray and the example worked with textures and everything (although it looked odd) because I was supposed to use the indices array.
When I switched to glDrawElements, the app crashed on glDrawElements. What is the proper way to debug such a problem?

Related

OpenGL - ES drawing and blending

I'm developing program that is described below.
I draw two triangles with different depths.
For below example, I'd like to split green triangle to visible part and hidden part. Then, finally using blending function, the hidden part of the green triangle is colored as transparent, and visible part is colored as original color.
Now, I write codes using opengl-ES (with JNI).
And, I have two questions.
First :
glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
glClear( GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
glUseProgram(gProgram);
glGetUniformLocation(gProgram, "vColor");
const GLfloat gTriangleVertices1[] =
{
-0.5f, -0.5f, -0.5f,
0.0f, 0.5f, -0.5f,
0.5f, -0.5f, -0.5f,
};
float color1[] = {1.0f, 0.0f, 0.0f};
const GLfloat gTriangleVertices2[] =
{
-0.7f, 0.0f, 0.3f,
0.5f, 0.3f, 0.3f,
0.5f, 0.0f, 0.3f,
};
float color2[] = {0.0f, 1.0f, 0.0f};
int mColorHandle1;
int mColorHandle2;
glEnable(GL_BLEND);
glEnable(GL_DEPTH_TEST);
glClearDepthf(1.0f);
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
glUniform4f(mColorHandle1, color1[0], color1[1], color1[2], color1[3]);
glVertexAttribPointer(gvPositionHandle, 3, GL_FLOAT, GL_FALSE, 0, gTriangleVertices1);
glEnableVertexAttribArray(gvPositionHandle);
glDrawArrays(GL_TRIANGLES, 0, 3);
glDepthFunc(GL_GREATER);
//glDepthFunc(GL_LESS);
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glUniform4f(mColorHandle2, color2[0], color2[1], color2[2], color2[3]);
glDrawArrays(GL_TRIANGLES, 3, 3);
glDisableVertexAttribArray(gvPositionHandle);
from this code, if I change glDepthFunc(GL_GREATER) to glDepthFunc(GL_LESS), the result shows visible and hidden part correctly.
However, I do not understand why it shows correct answer.
Because, I added vertex gTriangleVertices1, but I do not add gTriangleVertices2.
Even thou I do not add vertices of triangle 2, It gives me correct answer. why?
Second question, I think it is correct to use blending function (I checked it works on glut / freeglut). but why it doesn't work on gl-es.
///////////////////////// visible part /////////////////////////
glEnable(GL_BLEND);
glEnable(GL_DEPTH_TEST);
glClearDepthf(1.0f);
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
glUniform4f(mColorHandle1, color1[0], color1[1], color1[2], color1[3]);
glVertexAttribPointer(gvPositionHandle, 3, GL_FLOAT, GL_FALSE, 0, gTriangleVertices1);
glEnableVertexAttribArray(gvPositionHandle);
glDrawArrays(GL_TRIANGLES, 0, 3);
glDepthFunc(GL_LESS);
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glUniform4f(mColorHandle2, color2[0], color2[1], color2[2], color2[3]);
glDrawArrays(GL_TRIANGLES, 3, 3);
glDisableVertexAttribArray(gvPositionHandle);
glDisable(GL_DEPTH_TEST);
glDepthFunc(GL_LESS); // same to initialize depth func
///////////////////////// visible part /////////////////////////
///////////////////////// hidden part /////////////////////////
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glEnable(GL_DEPTH_TEST);
glClearDepthf(1.0f);
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
glUniform4f(mColorHandle1, color1[0], color1[1], color1[2], color1[3]);
glVertexAttribPointer(gvPositionHandle, 3, GL_FLOAT, GL_FALSE, 0, gTriangleVertices1);
glEnableVertexAttribArray(gvPositionHandle);
glDrawArrays(GL_TRIANGLES, 0, 3);
glDepthFunc(GL_GREATER);
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glUniform4f(mColorHandle2, color2[0], color2[1], color2[2], 0.5f);
glDrawArrays(GL_TRIANGLES, 3, 3);
glDisableVertexAttribArray(gvPositionHandle);
///////////////////////// hidden part /////////////////////////
I just added blending function. If I uses visible/hidden part alone, it gives correct result. However if I use blending function, it gives strange result as shown below : it gives transparent hidden green triangle.
what's wrong?
The first question:
You created a major bug by saying glDrawArrays(GL_TRIANGLES, 3, 3); as this produces an overflow on your buffer. The result of it is unexpected but in your case your compiler seems to have decided that the two arrays you defined are tightly packed:
const GLfloat gTriangleVertices1[] =
{
-0.5f, -0.5f, -0.5f,
0.0f, 0.5f, -0.5f,
0.5f, -0.5f, -0.5f,
};
const GLfloat gTriangleVertices2[] =
{
-0.7f, 0.0f, 0.3f,
0.5f, 0.3f, 0.3f,
0.5f, 0.0f, 0.3f,
};
And are considered as
const GLfloat gTriangleVertices[] =
{
-0.5f, -0.5f, -0.5f,
0.0f, 0.5f, -0.5f,
0.5f, -0.5f, -0.5f,
-0.7f, 0.0f, 0.3f,
0.5f, 0.3f, 0.3f,
0.5f, 0.0f, 0.3f,
};
So the overflow actually jumps to the part of the memory where the second vertex data is. Make no mistake of thinking what you did is correct by mistake. It is not correct and this can break on different version or for any other reason, platform, device... So fix it.
The second question:
The blending and depth buffer do not go together. You need to avoid this combination. I will not explain the reasons here (search a bit for it) but the result is undefined and you may not use that. Use one or the other.
If you will search the web on how to tackle this you will not find a correct answer for your situation though as it is very unique. What I suggest for the general solution for your case is to add a stencil buffer.
The first call should also draw to the stencil buffer which is then used to draw in the last call as well. So the last call should have a depth test disabled but stencil enabled. But doing that you should most likely simply remove the depth and use stencil only.
I am sure there are other possible solutions to this by using an alpha channel as well but in any case remember that depth buffer combined with blending is strictly forbidden and the behavior is undefined. It means it can even vary between the GPUs.

Backside color of CCTransitionPageTurn in Cocos2d-x 2.0

How can I specify the color of backside of a scene when I use CCTransitionPageTurn? In cocos2d-iphone 1.0, I did some modifications in blot() in CCGrid.m like this:
NSInteger n = gridSize_.x * gridSize_.y;
// Default GL states: GL_TEXTURE_2D, GL_VERTEX_ARRAY, GL_COLOR_ARRAY, GL_TEXTURE_COORD_ARRAY
// Needed states: GL_TEXTURE_2D, GL_VERTEX_ARRAY, GL_TEXTURE_COORD_ARRAY
// Unneeded states: GL_COLOR_ARRAY
//enable culling, the default cull face is back
glEnable(GL_CULL_FACE);
//now only the front facing polygons are drawn
glDisableClientState(GL_COLOR_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, vertices);
glTexCoordPointer(2, GL_FLOAT, 0, texCoordinates);
glDrawElements(GL_TRIANGLES, (GLsizei) n*6, GL_UNSIGNED_SHORT, indices);
// This is very important, otherwise the backside of picture will be random color
glDisable(GL_TEXTURE_2D);
//change the winding of what OpenGl considers front facing
//only the back facing polygons will be drawn
//this works better then changing the cull face
glFrontFace(GL_CW);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glColor4ub(255,255,255,255);
glDrawElements(GL_TRIANGLES, (GLsizei) n*6, GL_UNSIGNED_SHORT, indices);
//restore GL default states
glFrontFace(GL_CCW);
glDisable(GL_CULL_FACE);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glEnableClientState(GL_COLOR_ARRAY);
This is cpp code, I think I can use in cocos2d-x. But unfortunately, this code doesn't work for 2.0. Can anybody suggest how to translate this to 2.0 ? Or is there alternative way to set color in backside of a scene during CCTransitionPageTurn?
Basing on your snippet and other google searches I've managed to achieve this :
void CCGrid3D::blit(void)
{
CCLOG("CCGrid3D::blit()");
int n = m_sGridSize.width * m_sGridSize.height;
ccGLEnableVertexAttribs( kCCVertexAttribFlag_Position | kCCVertexAttribFlag_TexCoords );
m_pShaderProgram->use();
m_pShaderProgram->setUniformsForBuiltins();;
//
// Attributes
//
#ifdef EMSCRIPTEN
// Size calculations from calculateVertexPoints().
unsigned int numOfPoints = (m_sGridSize.width+1) * (m_sGridSize.height+1);
// position
setGLBufferData(m_pVertices, numOfPoints * sizeof(ccVertex3F), 0);
glVertexAttribPointer(kCCVertexAttrib_Position, 3, GL_FLOAT, GL_FALSE, 0, 0);
// texCoords
setGLBufferData(m_pTexCoordinates, numOfPoints * sizeof(ccVertex2F), 1);
glVertexAttribPointer(kCCVertexAttrib_TexCoords, 2, GL_FLOAT, GL_FALSE, 0, 0);
setGLIndexData(m_pIndices, n * 12, 0);
glDrawElements(GL_TRIANGLES, (GLsizei) n*6, GL_UNSIGNED_SHORT, 0);
#else
glEnable(GL_CULL_FACE);
glVertexAttribPointer(kCCVertexAttrib_Position, 3, GL_FLOAT, GL_FALSE, 0, m_pVertices);
glVertexAttribPointer(kCCVertexAttrib_TexCoords, 2, GL_FLOAT, GL_FALSE, 0, m_pTexCoordinates);
glDrawElements(GL_TRIANGLES, (GLsizei)n*6, GL_UNSIGNED_SHORT, m_pIndices);
glDisable(GL_TEXTURE_2D);
glFrontFace(GL_CW);
ccGLEnableVertexAttribs(kCCVertexAttribFlag_Position);
glEnable(GL_BLEND);
glDrawElements(GL_TRIANGLES, (GLsizei)n*6, GL_UNSIGNED_SHORT, m_pIndices);
glFrontFace(GL_CCW);
glDisable(GL_BLEND);
glDisable(GL_CULL_FACE);
#endif // EMSCRIPTEN
CC_INCREMENT_GL_DRAWS(1);
}
It has only one drawback : it does not let you specify the back color, but rather it gets the color of the bottom-left pixel and uses it. I hope this is enough for you, or that you will be able to change this so that it will let us specify the color needed.

thread 1 :program received signal exc_bad_access?

currently i am working in simple game app, using GL_TRIANGLE_STRIP to draw a ball image (Moving left to right) and using GL_LINES to draw a line in Touch began Delegate, when i touch the screen app will quit like program received signal exc_bad_access, i spend 14 hours but i cannot fix this, please help me any one.
Thanks in Advance
I tried the source code:
-(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
Test =YES;
[self.effect prepareToDraw];
const GLfloat line[] =
{
0, 2,
0,-3,
};
GLuint bufferObjectNameArray;
glGenBuffers(1, &bufferObjectNameArray);
glBindBuffer(GL_ARRAY_BUFFER, bufferObjectNameArray);
glBufferData(
GL_ARRAY_BUFFER, // the target buffer
sizeof(line), // the number of bytes to put into the buffer
line, // a pointer to the data being copied
GL_STATIC_DRAW); // the usage pattern of the data
glEnableVertexAttribArray(GLKVertexAttribPosition);
glVertexAttribPointer(
GLKVertexAttribPosition, // the currently bound buffer holds the data
2, // number of coordinates per vertex
GL_FLOAT, // the data type of each component
GL_FALSE, // can the data be scaled
2*4, // how many bytes per vertex (2 floats per vertex)
NULL); // offset to the first coordinate, in this case 0
glDrawArrays(GL_Lines,0,3);
}
- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect
{
glClearColor(1, 1, 1, 1);
glClear(GL_COLOR_BUFFER_BIT);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glEnable(GL_BLEND);
NSLog(#"Children count:%d",[self.children count]); // Store ball image in NSMutable array
for (SGGSprite * sprite in self.children)
{
self.effect.texture2d0.name = self.textureInfo.name;
self.effect.texture2d0.enabled = YES;
GLKMatrix4 modelMatrix = GLKMatrix4Identity;
modelMatrix = GLKMatrix4Translate(modelMatrix, -self.position.x, -self.position.y, 0);
modelMatrix = GLKMatrix4Translate(modelMatrix, self.contentSize.width, self.contentSize.height+140, 0);
return modelMatrix;
[self.effect prepareToDraw];
long offset = (long)&_quad;
glEnableVertexAttribArray(GLKVertexAttribPosition);
glEnableVertexAttribArray(GLKVertexAttribTexCoord0);
NSLog(#"TexturedVertex:%ld",offset);
glVertexAttribPointer(GLKVertexAttribPosition, 2, GL_FLOAT, GL_FALSE, sizeof(TexturedVertex), (void *) (offset + offsetof(TexturedVertex, geometryVertex)));
glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, sizeof(TexturedVertex), (void *) (offset + offsetof(TexturedVertex, textureVertex)));
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); // When i tab the screen, the app will quit in this line like thread 1 :program received signal exc_bad_access.
}
}

Open GLES 1.1 - GLColorPointer creates a rainbow of colours when I just want red

I'm rendering an object like this:
for (int i = 0; i < COLOR_ARRAY_SIZE; i += 4) {
colors[i] = 1.0f;
colors[i + 1] = 0.0f;
colors[i + 2] = 0.0f;
colors[i + 3] = 1.0f;
}
// Clear color and depth buffer
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Set GL11 flags:
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_NORMAL_ARRAY);
glEnableClientState(GL_COLOR_ARRAY);
glEnable(GL_DEPTH_TEST);
// make sure nothing messes with the colour
glDisable(GL_BLEND);
glDisable(GL_DITHER);
glDisable(GL_FOG);
glDisable(GL_LIGHTING);
glDisable(GL_TEXTURE_2D);
glShadeModel(GL_FLAT);
// Load projection matrix:
glMatrixMode(GL_PROJECTION);
glLoadMatrixf(projectionMatrix);
// Load model view matrix and scale appropriately
int kObjectScale = 300f;
glMatrixMode(GL_MODELVIEW);
glLoadMatrixf(modelViewMatrix);
glTranslatef(0.5f, 0.5f, 0.5f);
glScalef(kObjectScale, kObjectScale, kObjectScale);
// Draw object
glVertexPointer(3, GL_FLOAT, 0, (const GLvoid*) &vertexPositions[0]);
glNormalPointer(GL_FLOAT, 0, (const GLvoid*) &vertexNormals[0]);
glColorPointer(4, GL_FLOAT, 0, (const GLvoid*) &colors[0]);
glDrawElements(GL_TRIANGLES, 11733, GL_UNSIGNED_SHORT,
(const GLvoid*) &indices[0]);
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_NORMAL_ARRAY);
glDisableClientState(GL_COLOR_ARRAY);
I would expect that this would render my object all in red, but instead it's a rainbow of different colours. Does anyone know why? I would assume that there is something wrong with my "colors" array buffer but I can't for the life of me see what it is. The actual vertices seem to rendered just fine.
Your for loop is very confused. You're incrementing your value of i by 4 each time. What's more is that you're indexing with an offset of 1, 2 and 3 in lines 3-5. I presume that your define of COLOR_ARRAY_SIZE is 4? Try initializing your color array as follows:
float colors[] = {1.0f, 0.0f, 0.0f, 1.0f};
And then calling glColorPointer as follows:
glColorPointer(4, GL_FLOAT, 0, colors);
Notice that I've set the stride to be 0. If your color array only contains colors then I don't see any reason why you should be using a stride (stride is used to jump over interwoven information in an array).

Rendering 2D sprites in a 3D world?

How do I render 2D sprites in OpenGL given that I have a png of the sprite? See images as an example of the effect I'd like to achieve. Also I would like to overlay weapons on the screen like the rifle in the bottom image. Does anyone know how I would achieve the two effects? Any help is greatly appreciated.
In 3D terms, this is called a "billboard". A billboard is completely flat 2D plane with a texture on it and it always faces the camera.
See here for a pure OpenGL implementation: http://nehe.gamedev.net/data/articles/article.asp?article=19
Just about any 3D engine should be able to do them by default. Ogre3D can do it, for instance.
a) For the first case:
That's not really 2D sprites. Those men seem to be rendered as single quads with a texture with some kind of transparency (either alpha test or alpha blending).
Anyway, even a single quad can still be considered a 3D object, so for such situation you might want to treat it as one: track its translation and rotation and render it in the same way as any other 3D object.
b) For the second case:
If you want the gun (a 2D picture, I pressume) to be rendered in the same place without any perspective transformation, then you can use the same technique one uses for drawing the GUI (etc). Have a look at my post here:
2D overlay on a 3D scene
For the overlaying of the 2D weapon, you can use glOrtho for the camera view.
You create a 3d quad and map the .png-based texture to it. You can make the quad face whatever direction you want, as in the first picture, or make it always facing the camera (like a billboard, mentioned by Svenstaro) as in your second picture. Though, to be fair, I am sure that second picture just blitted the image (with some scaling) directly in the software-created framebuffer (that looks like Wolf3d tech, software rendering).
Take a look at OpenGL Point Sprites:
http://www.informit.com/articles/article.aspx?p=770639&seqNum=7
Especially useful for partical systems but may do the trick for your purposes.
Check this tutorial about billboards. I think you'll find useful.
http://www.lighthouse3d.com/opengl/billboarding/
opengl-tutorial has:
a tutorial http://www.opengl-tutorial.org/intermediate-tutorials/billboards-particles/billboards/ focused on energy bars
OpenGL 3.3+ WTF licensed code that just works: https://github.com/opengl-tutorials/ogl/blob/71cad106cefef671907ba7791b28b19fa2cc034d/tutorial18_billboards_and_particles/tutorial18_billboards.cpp
Screenshot:
Code:
#include <stdio.h>
#include <stdlib.h>
#include <vector>
#include <algorithm>
#include <GL/glew.h>
#include <glfw3.h>
GLFWwindow* window;
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtx/norm.hpp>
using namespace glm;
#include <common/shader.hpp>
#include <common/texture.hpp>
#include <common/controls.hpp>
#define DRAW_CUBE // Comment or uncomment this to simplify the code
int main( void )
{
// Initialise GLFW
if( !glfwInit() )
{
fprintf( stderr, "Failed to initialize GLFW\n" );
getchar();
return -1;
}
glfwWindowHint(GLFW_SAMPLES, 4);
glfwWindowHint(GLFW_RESIZABLE,GL_FALSE);
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // To make MacOS happy; should not be needed
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
// Open a window and create its OpenGL context
window = glfwCreateWindow( 1024, 768, "Tutorial 18 - Billboards", NULL, NULL);
if( window == NULL ){
fprintf( stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n" );
getchar();
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(window);
// Initialize GLEW
glewExperimental = true; // Needed for core profile
if (glewInit() != GLEW_OK) {
fprintf(stderr, "Failed to initialize GLEW\n");
getchar();
glfwTerminate();
return -1;
}
// Ensure we can capture the escape key being pressed below
glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);
// Hide the mouse and enable unlimited mouvement
glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);
// Set the mouse at the center of the screen
glfwPollEvents();
glfwSetCursorPos(window, 1024/2, 768/2);
// Dark blue background
glClearColor(0.0f, 0.0f, 0.4f, 0.0f);
// Enable depth test
glEnable(GL_DEPTH_TEST);
// Accept fragment if it closer to the camera than the former one
glDepthFunc(GL_LESS);
GLuint VertexArrayID;
glGenVertexArrays(1, &VertexArrayID);
glBindVertexArray(VertexArrayID);
// Create and compile our GLSL program from the shaders
GLuint programID = LoadShaders( "Billboard.vertexshader", "Billboard.fragmentshader" );
// Vertex shader
GLuint CameraRight_worldspace_ID = glGetUniformLocation(programID, "CameraRight_worldspace");
GLuint CameraUp_worldspace_ID = glGetUniformLocation(programID, "CameraUp_worldspace");
GLuint ViewProjMatrixID = glGetUniformLocation(programID, "VP");
GLuint BillboardPosID = glGetUniformLocation(programID, "BillboardPos");
GLuint BillboardSizeID = glGetUniformLocation(programID, "BillboardSize");
GLuint LifeLevelID = glGetUniformLocation(programID, "LifeLevel");
GLuint TextureID = glGetUniformLocation(programID, "myTextureSampler");
GLuint Texture = loadDDS("ExampleBillboard.DDS");
// The VBO containing the 4 vertices of the particles.
static const GLfloat g_vertex_buffer_data[] = {
-0.5f, -0.5f, 0.0f,
0.5f, -0.5f, 0.0f,
-0.5f, 0.5f, 0.0f,
0.5f, 0.5f, 0.0f,
};
GLuint billboard_vertex_buffer;
glGenBuffers(1, &billboard_vertex_buffer);
glBindBuffer(GL_ARRAY_BUFFER, billboard_vertex_buffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_DYNAMIC_DRAW);
#ifdef DRAW_CUBE
// Everything here comes from Tutorial 4
GLuint cubeProgramID = LoadShaders( "../tutorial04_colored_cube/TransformVertexShader.vertexshader", "../tutorial04_colored_cube/ColorFragmentShader.fragmentshader" );
GLuint cubeMatrixID = glGetUniformLocation(cubeProgramID, "MVP");
static const GLfloat g_cube_vertex_buffer_data[] = { -1.0f,-1.0f,-1.0f,-1.0f,-1.0f, 1.0f,-1.0f, 1.0f, 1.0f,1.0f, 1.0f,-1.0f,-1.0f,-1.0f,-1.0f,-1.0f, 1.0f,-1.0f,1.0f,-1.0f, 1.0f,-1.0f,-1.0f,-1.0f,1.0f,-1.0f,-1.0f,1.0f, 1.0f,-1.0f,1.0f,-1.0f,-1.0f,-1.0f,-1.0f,-1.0f,-1.0f,-1.0f,-1.0f,-1.0f, 1.0f, 1.0f,-1.0f, 1.0f,-1.0f,1.0f,-1.0f, 1.0f,-1.0f,-1.0f, 1.0f,-1.0f,-1.0f,-1.0f,-1.0f, 1.0f, 1.0f,-1.0f,-1.0f, 1.0f,1.0f,-1.0f, 1.0f,1.0f, 1.0f, 1.0f,1.0f,-1.0f,-1.0f,1.0f, 1.0f,-1.0f,1.0f,-1.0f,-1.0f,1.0f, 1.0f, 1.0f,1.0f,-1.0f, 1.0f,1.0f, 1.0f, 1.0f,1.0f, 1.0f,-1.0f,-1.0f, 1.0f,-1.0f,1.0f, 1.0f, 1.0f,-1.0f, 1.0f,-1.0f,-1.0f, 1.0f, 1.0f,1.0f, 1.0f, 1.0f,-1.0f, 1.0f, 1.0f,1.0f,-1.0f, 1.0f};
static const GLfloat g_cube_color_buffer_data[] = { 0.583f, 0.771f, 0.014f,0.609f, 0.115f, 0.436f,0.327f, 0.483f, 0.844f,0.822f, 0.569f, 0.201f,0.435f, 0.602f, 0.223f,0.310f, 0.747f, 0.185f,0.597f, 0.770f, 0.761f,0.559f, 0.436f, 0.730f,0.359f, 0.583f, 0.152f,0.483f, 0.596f, 0.789f,0.559f, 0.861f, 0.639f,0.195f, 0.548f, 0.859f,0.014f, 0.184f, 0.576f,0.771f, 0.328f, 0.970f,0.406f, 0.615f, 0.116f,0.676f, 0.977f, 0.133f,0.971f, 0.572f, 0.833f,0.140f, 0.616f, 0.489f,0.997f, 0.513f, 0.064f,0.945f, 0.719f, 0.592f,0.543f, 0.021f, 0.978f,0.279f, 0.317f, 0.505f,0.167f, 0.620f, 0.077f,0.347f, 0.857f, 0.137f,0.055f, 0.953f, 0.042f,0.714f, 0.505f, 0.345f,0.783f, 0.290f, 0.734f,0.722f, 0.645f, 0.174f,0.302f, 0.455f, 0.848f,0.225f, 0.587f, 0.040f,0.517f, 0.713f, 0.338f,0.053f, 0.959f, 0.120f,0.393f, 0.621f, 0.362f,0.673f, 0.211f, 0.457f,0.820f, 0.883f, 0.371f,0.982f, 0.099f, 0.879f};
GLuint cubevertexbuffer;
glGenBuffers(1, &cubevertexbuffer);
glBindBuffer(GL_ARRAY_BUFFER, cubevertexbuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(g_cube_vertex_buffer_data), g_cube_vertex_buffer_data, GL_DYNAMIC_DRAW);
GLuint cubecolorbuffer;
glGenBuffers(1, &cubecolorbuffer);
glBindBuffer(GL_ARRAY_BUFFER, cubecolorbuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(g_cube_color_buffer_data), g_cube_color_buffer_data, GL_DYNAMIC_DRAW);
#endif
double lastTime = glfwGetTime();
do
{
// Clear the screen
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
double currentTime = glfwGetTime();
double delta = currentTime - lastTime;
lastTime = currentTime;
computeMatricesFromInputs();
glm::mat4 ProjectionMatrix = getProjectionMatrix();
glm::mat4 ViewMatrix = getViewMatrix();
#ifdef DRAW_CUBE
// Again : this is just Tutorial 4 !
glDisable(GL_BLEND);
glUseProgram(cubeProgramID);
glm::mat4 cubeModelMatrix(1.0f);
cubeModelMatrix = glm::scale(cubeModelMatrix, glm::vec3(0.2f, 0.2f, 0.2f));
glm::mat4 cubeMVP = ProjectionMatrix * ViewMatrix * cubeModelMatrix;
glUniformMatrix4fv(cubeMatrixID, 1, GL_FALSE, &cubeMVP[0][0]);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, cubevertexbuffer);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0 );
glEnableVertexAttribArray(1);
glBindBuffer(GL_ARRAY_BUFFER, cubecolorbuffer);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, (void*)0 );
glDrawArrays(GL_TRIANGLES, 0, 12*3);
glDisableVertexAttribArray(0);
glDisableVertexAttribArray(1);
#endif
// We will need the camera's position in order to sort the particles
// w.r.t the camera's distance.
// There should be a getCameraPosition() function in common/controls.cpp,
// but this works too.
glm::vec3 CameraPosition(glm::inverse(ViewMatrix)[3]);
glm::mat4 ViewProjectionMatrix = ProjectionMatrix * ViewMatrix;
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
// Use our shader
glUseProgram(programID);
// Bind our texture in Texture Unit 0
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, Texture);
// Set our "myTextureSampler" sampler to user Texture Unit 0
glUniform1i(TextureID, 0);
// This is the only interesting part of the tutorial.
// This is equivalent to mlutiplying (1,0,0) and (0,1,0) by inverse(ViewMatrix).
// ViewMatrix is orthogonal (it was made this way),
// so its inverse is also its transpose,
// and transposing a matrix is "free" (inversing is slooow)
glUniform3f(CameraRight_worldspace_ID, ViewMatrix[0][0], ViewMatrix[1][0], ViewMatrix[2][0]);
glUniform3f(CameraUp_worldspace_ID , ViewMatrix[0][1], ViewMatrix[1][1], ViewMatrix[2][1]);
glUniform3f(BillboardPosID, 0.0f, 0.5f, 0.0f); // The billboard will be just above the cube
glUniform2f(BillboardSizeID, 1.0f, 0.125f); // and 1m*12cm, because it matches its 256*32 resolution =)
// Generate some fake life level and send it to glsl
float LifeLevel = sin(currentTime)*0.1f + 0.7f;
glUniform1f(LifeLevelID, LifeLevel);
glUniformMatrix4fv(ViewProjMatrixID, 1, GL_FALSE, &ViewProjectionMatrix[0][0]);
// 1rst attribute buffer : vertices
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, billboard_vertex_buffer);
glVertexAttribPointer(
0, // attribute. No particular reason for 0, but must match the layout in the shader.
3, // size
GL_FLOAT, // type
GL_FALSE, // normalized?
0, // stride
(void*)0 // array buffer offset
);
// Draw the billboard !
// This draws a triangle_strip which looks like a quad.
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glDisableVertexAttribArray(0);
// Swap buffers
glfwSwapBuffers(window);
glfwPollEvents();
} // Check if the ESC key was pressed or the window was closed
while( glfwGetKey(window, GLFW_KEY_ESCAPE ) != GLFW_PRESS &&
glfwWindowShouldClose(window) == 0 );
// Cleanup VBO and shader
glDeleteBuffers(1, &billboard_vertex_buffer);
glDeleteProgram(programID);
glDeleteTextures(1, &TextureID);
glDeleteVertexArrays(1, &VertexArrayID);
#ifdef DRAW_CUBE
glDeleteProgram(cubeProgramID);
glDeleteVertexArrays(1, &cubevertexbuffer);
glDeleteVertexArrays(1, &cubecolorbuffer);
#endif
// Close OpenGL window and terminate GLFW
glfwTerminate();
return 0;
}
Tested on Ubuntu 15.10.
Axis oriented version of this question: https://gamedev.stackexchange.com/questions/35946/how-do-i-implement-camera-axis-aligned-billboards Here we have done a viewpoint oriented billboard.

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