I have a cube which I want to rotate. I also have a light source GL_LIGHT0. I want to rotate the cube and leave the light source fixed in its location. But the light source is rotating together with my cube. I use OpenGL ES 1.1
Here's a snippet of my code to make my question more clear.
GLfloat glfarr[] = {...} //cube points
GLubyte glubFaces[] = {...}
Vertex3D normals[] = {...} //normals to surfaces
const GLfloat light0Position[] = {0.0, 0.0, 3.0, 0.0};
glLightfv(GL_LIGHT0, GL_POSITION, light0Position);
glEnable(GL_LIGHT0);
for(i = 0; i < 8000; ++i)
{
if (g_bDemoDone) break;
glLoadIdentity();
glTranslatef(0.0,0.0, -12);
glRotatef(rot, 0.0, 1.0,1.0);
rot += 0.8;
glClearColor(0, 0, 0, 1);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_NORMAL_ARRAY);
glNormalPointer(GL_FLOAT, 0, normals);
glVertexPointer(3, GL_FLOAT, 0, glfarr);
glDrawElements(GL_TRIANGLES, 3*12, GL_UNSIGNED_BYTE, glubFaces);
glDisableClientState(GL_NORMAL_ARRAY);
glDisableClientState(GL_VERTEX_ARRAY);
eglSwapBuffers(eglDisplay, eglSurface);
}
Thanks.
Fixed in relation to what? The light position is transformed by the current MODELVIEW matrix when you do glLightfv(GL_LIGHT0, GL_POSITION, light0Position);
If you want it to move with with the cube you'll have to move glLightfv(GL_LIGHT0, GL_POSITION, light0Position); to after the translation and rotation calls.
The problem seems to be that you're rotating the modelview matrix, not the cube itself. Essentially, you're moving the camera.
In order to rotate just the cube, you'll need to rotate the vertices that make up the cube. Generally that's done using a library (GLUT or some such) or simple trig. You'll be operating on the vertex data stored in the array, before the glDrawElements call. You may/may not have to or want to modify the normals or texture coordinates, it depends on your effects and how it ends up looking.
Related
I'm working on a little 2D graphics/game library for personal use and currently I'm trying to think of a way to improve performance when drawing tiled maps. Currently I am creating a static GL_QUADS VBO for each tile in the map and then drawing it to the screen. Each VBO is referencing a texture loaded into memory which is sub-imaged and mapped to the VBO.
Currently, I have a 20 x 20 tile map that I am testing with. With my current implementation, since I have to draw each individual tile, that is 400 glDraw* calls every frame.
Is there any way to, for example, make each row of the tile map ONE VBO? This would reduce the glDraw* calls to 20, for this example. How would I map the sub-images? Individual tiles can be rotated.
I have seen some references to using a Texture Atlas. Would that be a good alternative? Any useful links on how to implement this in opengl?
CODE:
Current render method:
public void render() {
texture.bind();
glEnable(GL_TEXTURE_2D);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_COLOR_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
for (SpriteSheet spriteSheet : spriteSheets) {
VBO vbo = spriteSheet.getVBO();
float angle = spriteSheet.getAngle();
vbo.bind();
if (angle != 0) {
glPushMatrix();
Vector2f position = spriteSheet.getPosition();
glTranslatef(position.x, position.y, 0);
glRotatef(angle, 0.0f, 0.0f, 1);
glTranslatef(-position.x, -position.y, 0);
glVertexPointer(Vertex.positionElementCount, GL_FLOAT, Vertex.stride, Vertex.positionByteOffset);
glColorPointer(Vertex.colorElementCount, GL_FLOAT, Vertex.stride, Vertex.colorByteOffset);
glTexCoordPointer(Vertex.textureElementCount, GL_FLOAT, Vertex.stride, Vertex.textureByteOffset);
glDrawArrays(vbo.getMode(), 0, Vertex.elementCount);
glPopMatrix();
}
else {
glVertexPointer(Vertex.positionElementCount, GL_FLOAT, Vertex.stride, Vertex.positionByteOffset);
glColorPointer(Vertex.colorElementCount, GL_FLOAT, Vertex.stride, Vertex.colorByteOffset);
glTexCoordPointer(Vertex.textureElementCount, GL_FLOAT, Vertex.stride, Vertex.textureByteOffset);
glDrawArrays(vbo.getMode(), 0, Vertex.elementCount);
}
vbo.unbind();
}
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glDisableClientState(GL_COLOR_ARRAY);
glDisableClientState(GL_VERTEX_ARRAY);
glDisable(GL_BLEND);
glDisable(GL_TEXTURE_2D);
texture.unbind();
}
There are several things you can do.
A texture atlas one option, but you could use a GL_TEXTURE_2D_ARRAY as well, using the 3rd texture coordinate to select which layer to use.
The next thing to think about is instancing: Have a single quad in the buffer and make OpenGL draw it several times, using an additional buffer to select texture layer and rotation based on the drawn instance.
I am using this simple function to draw quad in 3D space that is facing camera. Now, I want to use fragment shader to draw illusion of a sphere inside. But, the problem is I'm new to OpenGL ES, so I don't know how?
void draw_sphere(view_t view) {
set_gl_options(COURSE);
glPushMatrix();
{
glTranslatef(view.plyr_pos.x, view.plyr_pos.y, view.plyr_pos.z - 1.9);
#ifdef __APPLE__
#undef glEnableClientState
#undef glDisableClientState
#undef glVertexPointer
#undef glTexCoordPointer
#undef glDrawArrays
static const GLfloat vertices []=
{
0, 0, 0,
1, 0, 0,
1, 1, 0,
0, 1, 0,
0, 0, 0,
1, 1, 0
};
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, vertices);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 6);
glDisableClientState(GL_VERTEX_ARRAY);
#else
#endif
}
glPopMatrix();
}
More exactly, I want to achieve this:
There might be quite a few thing you need to to achieve this... The sphere that is drawn on the last image you posted is a result in using lighting and shine and color. In general you need a shader that can process all that and can normally work for any shape.
This specific case (also some others that can be mathematically presented) can be drawn with a single quad without even needing to push normal coordinates to the program. What you need to do is create a normal in a fragment shader: If you receive vectors sphereCenter, fragmentPosition and float sphereRadius, then sphereNormal is a vector such as
sphereNormal = (fragmentPosition-sphereCenter)/radius; //taking into account all have .z = .0
sphereNormal.z = -sqrt(1.0 - length(sphereNormal)); //only if(length(spherePosition) < sphereRadius)
and real sphere position:
spherePosition = sphereCenter + sphereNormal*sphereRadius;
Now all you need to do is add your lighting.. Static or not it is most common to use some ambient factor, linear and square distance factors, shine factor:
color = ambient*materialColor; //apply ambient
vector fragmentToLight = lightPosition-spherePosition;
float lightDistance = length(fragmentToLight);
fragmentToLight = normalize(fragmentToLight); //can also just divide with light distance
float dotFactor = dot(sphereNormal, fragmentToLight); //dot factor is used to take int account the angle between light and surface normal
if(dotFactor > .0) {
color += (materialColor*dotFactor)/(1.0 + lightDistance*linearFactor + lightDistance*lightDistance*squareFactor); //apply dot factor and distance factors (in many cases the distance factors are 0)
}
vector shineVector = (sphereNormal*(2.0*dotFactor)) - fragmentToLight; //this is a vector that is mirrored through the normal, it is a reflection vector
float shineFactor = dot(shineVector, normalize(cameraPosition-spherePosition)); //factor represents how strong is the light reflection towards the viewer
if(shineFactor > .0) {
color += materialColor*(shineFactor*shineFactor * shine); //or some other power then 2 (shineFactor*shineFactor)
}
This pattern to create lights in fragment shader is one of very many. If you don't like it or you cant make it work I suggest you find another one on the web, otherwise I hope you will understand it and be able to play around with it.
I am teaching myself about open gl es and vertex buffer (VBO) and I have written code and it is supposed to draw one red triangle but instead it colours the screen black:
- (void)drawRect:(CGRect)rect {
// Draw a red triangle in the middle of the screen:
glColor4f(1.0f, 0.0f, 0.0f, 1.0f);
// Setup the vertex data:
typedef struct {
float x;
float y;
} Vertex;
const Vertex vertices[] = {{50,50}, {50,150}, {150,50}};
const short indices[3] = {0,1,2};
glGenBuffers(1, &vertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
NSLog(#"drawrect");
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, 0);
// The following line does the actual drawing to the render buffer:
glDrawElements(GL_TRIANGLE_STRIP, 3, GL_UNSIGNED_SHORT, indices);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, framebuffer);
[eAGLcontext presentRenderbuffer:GL_RENDERBUFFER_OES];
}
Here vertexBuffer is of type GLuint. What is going wrong? Thanks for your help.
Your vertices dont have a Z component, try {{50,50,-100}, {50,150,-100}, {150,50,-100}}; (your camera by default looks down the Z axis so putting it in the -Z should put it on screen) if you cant see it still try smaller numbers, im not sure what your near and far draw cutoff distance is, and if its not even set i dont know what the default is. This might not be the only issue but its the only one i can see by just looking quickly at it.
You need to add
glViewport(0, 0, 320, 480);
where you create the frame buffer and set up the context.
And replace your call to glDrawElements with
glDrawArrays(GL_TRIANGLE_STRIP, ...);
This is OpenGL on iPhone 4.
Im drawing scene using light and materials. Here is snippet of my code:
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glFrustumf(-1, 1, -1, 1, -1, 1);
CGFloat ambientLight[] = { 0.5f, 0.5f, 0.5f, 1.0f };
CGFloat diffuseLight[] = { 1.0f, 1.0f, 1.0f, 1.0f };
CGFloat direction[] = { 0.0f, 0.0f, -20.0f, 0 };
glEnable(GL_LIGHT0);
glLightfv(GL_LIGHT0, GL_AMBIENT, ambientLight);
glLightfv(GL_LIGHT0, GL_DIFFUSE, diffuseLight);
glLightfv(GL_LIGHT0, GL_POSITION, direction);
glShadeModel(GL_FLAT);
glEnable(GL_LIGHTING);
glDisable(GL_COLOR_MATERIAL);
float blankColor[4] = {0,0,0,1};
float whiteColor[4] = {1,1,1,1};
float blueColor[4] = {0,0,1,1};
glMaterialfv(GL_FRONT, GL_DIFFUSE, blueColor);
glEnable(GL_CULL_FACE);
glVertexPointer(3, GL_FLOAT, 0, verts.pdata);
glEnableClientState(GL_VERTEX_ARRAY);
glNormalPointer(GL_FLOAT, 0, normals.pdata);
glEnableClientState(GL_NORMAL_ARRAY);
glDrawArrays (GL_TRIANGLES, 0, verts.size/3);
Problem is that instead of seeing BLUE diffuse color I see it white. It fades out if I rotate model's side but I can't understand why its not using my blue color.
BTW if I change glMaterialfv(GL_FRONT, GL_DIFFUSE, blueColor) to glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, blueColor) then I do see blue color. If I do it glMaterialfv(GL_FRONT, GL_DIFFUSE, blueColor); and then glMaterialfv(GL_BACK, GL_DIFFUSE, blueColor); I see white color again. So it looks like GL_FRONT_AND_BACK shows it but rest of combinations show white. Anyone can explain it to me?
This is because of clockwise
10.090 How does face culling work? Why doesn't it use the surface normal?
OpenGL face culling calculates the signed area of the filled primitive in window coordinate space. The signed area is positive when the window coordinates are in a counter-clockwise order and negative when clockwise. An app can use glFrontFace() to specify the ordering, counter-clockwise or clockwise, to be interpreted as a front-facing or back-facing primitive. An application can specify culling either front or back faces by calling glCullFace(). Finally, face culling must be enabled with a call to glEnable(GL_CULL_FACE); .
OpenGL uses your primitive's window space projection to determine face culling for two reasons. To create interesting lighting effects, it's often desirable to specify normals that aren't orthogonal to the surface being approximated. If these normals were used for face culling, it might cause some primitives to be culled erroneously. Also, a dot-product culling scheme could require a matrix inversion, which isn't always possible (i.e., in the case where the matrix is singular), whereas the signed area in DC space is always defined.
However, some OpenGL implementations support the GL_EXT_ cull_vertex extension. If this extension is present, an application may specify a homogeneous eye position in object space. Vertices are flagged as culled, based on the dot product of the current normal with a vector from the vertex to the eye. If all vertices of a primitive are culled, the primitive isn't rendered. In many circumstances, using this extension
from here
Also you can read here
In my Mac application, I define a rectangular texture based on YUV 4:2:2 data from an attached camera. Using standard vertex and texture coordinates, I can draw this to a rectangular area on the screen without any problems.
However, I would like to use a GLSL fragment shader to process these image frames on the GPU, and am having trouble passing in the rectangular video texture as a uniform to the fragment shader. When I attempt to do so, the texture simply reads as black.
The shader program compiles, links, and passes validation. I am receiving the proper address for the uniform from the shader program. Other uniforms, such as floating point values, pass in correctly and the fragment shader responds to changes in these values. The fragment shader receives the correct texture coordinates. I've also sprinkled my code liberally with glGetError() and seen no errors anywhere.
The vertex shader is as follows:
void main()
{
gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
gl_FrontColor = gl_Color;
gl_TexCoord[0] = gl_TextureMatrix[0] * gl_MultiTexCoord0;
}
and the fragment shader is as follows:
uniform sampler2D videoFrame;
void main()
{
gl_FragColor = texture2D(videoFrame, gl_TexCoord[0].st);
}
This should simply display the texture on my rectangular geometry.
The relevant drawing code is as follows:
static const GLfloat squareVertices[] = {
-1.0f, -1.0f,
1.0f, -1.0f,
-1.0f, 1.0f,
1.0f, 1.0f,
};
const GLfloat textureVertices[] = {
0.0, videoImageSize.height,
videoImageSize.width, videoImageSize.height,
0.0, 0.0,
videoImageSize.width, 0.0
};
CGLSetCurrentContext(glContext);
if(!readyToDraw)
{
[self initGL];
readyToDraw = YES;
}
glViewport(0, 0, (GLfloat)self.bounds.size.width, (GLfloat)self.bounds.size.height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glEnable(GL_TEXTURE_2D);
glGenTextures(1, &textureName);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_RECTANGLE_EXT, textureName);
glTexImage2D(GL_TEXTURE_RECTANGLE_EXT, 0, GL_RGBA, videoImageSize.width, videoImageSize.height, 0, GL_YCBCR_422_APPLE, GL_UNSIGNED_SHORT_8_8_REV_APPLE, videoTexture);
glUseProgram(filterProgram);
glUniform1i(uniforms[UNIFORM_VIDEOFRAME], 0);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glVertexPointer(2, GL_FLOAT, 0, squareVertices);
glTexCoordPointer(2, GL_FLOAT, 0, textureVertices);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
[super drawInCGLContext:glContext pixelFormat:pixelFormat forLayerTime:interval displayTime:timeStamp];
glDeleteTextures(1, &textureName);
This code resides within a CAOpenGLLayer, where the superclass's -drawInCGLContext:pixelFormat:forLayerTime: displayTime: simply runs glFlush().
The uniform address is read using code like the following:
uniforms[UNIFORM_VIDEOFRAME] = glGetUniformLocation(filterProgram, "videoFrame");
As I said, if I comment out the glUseProgram() and glUniform1i() lines, this textured rectangle draws properly. Leaving them in leads to a black rectangle being drawn.
What could be preventing my texture uniform from being passed into my fragment shader?
Not sure about the GLSL version you're using, but from 1.40 upwards there's the type sampler2DRect specifically for accessing non-power-of-two textures. Might be what you're looking for, however I don't know how rectangular textures were handled before glsl 1.40.