I have to know how to add color to the rectangle drawn with the below method (which i took from a sample here).. Its by setting the openGL color to some color. But i dont know how to do it. Some help would be appreciated.
-(void) ccDrawFilledRect
{
HelloWorld *gs = [(swipeAppDelegate*)[[UIApplication sharedApplication] delegate] gameScene];
CGPoint poli[]= {gs.StartPoint,CGPointMake(gs.StartPoint.x,gs.EndPoint.y),gs.EndPoint,CGPointMake(gs.EndPoint.x,gs.StartPoint.y)};
glDisable(GL_TEXTURE_2D);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glDisableClientState(GL_COLOR_ARRAY);
glVertexPointer(2, GL_FLOAT, 0, poli);
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
NSLog(#"openGL rectangles drawn !!");
// restore default state
glEnableClientState(GL_COLOR_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glEnable(GL_TEXTURE_2D);
}
NeHe has a lot of easy OpenGL tutorials. This one is on adding color http://nehe.gamedev.net/data/lessons/lesson.asp?lesson=03 . Make your you have colors and color buffers enabled.
Have you tried putting glColor3d(1, 0, 0) before glVertexPointer?
Related
I'm making an iPhone game that involves the use of GL_POINT to render a point. However, when the center of the point is off screen, I still want to draw whatever portion of the point that is still onscreen. Here is my code that I'm using to render the point.
-(void)render {
if (!fill || !outline || !active || dead)
return;
NSLog(#"rendering");
glPushMatrix();
glLoadIdentity();
glMultMatrixf(matrix);
glEnable(GL_BLEND);
glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glEnable(GL_SMOOTH);
glEnable(GL_POINT_SMOOTH);
glPointSize(scale.x*2);
[outline render];
glPointSize(2*(scale.x-kLineWidth));
[fill render];
glPopMatrix();
}
note that it logs "rendering" when it should be rendering, so this method is getting called properly.
and the [outline render] and [fill render] methods look like this
-(void)render {
// load arrays into the engine
glVertexPointer(vertexSize, GL_FLOAT, 0, vertexes);
glEnableClientState(GL_VERTEX_ARRAY);
glColorPointer(colorSize, GL_FLOAT, 0, colors);
glEnableClientState(GL_COLOR_ARRAY);
//render
glDrawArrays(renderStyle, 0, vertexCount);
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_COLOR_ARRAY);
}
and I'm using a "panning" effect using this code
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrthof(-kScreenWidth/2.0 + xPan, kScreenWidth/2.0 + xPan, -kScreenHeight/2.0 + yPan, kScreenHeight/2.0 + yPan, -1.0f, 1.0f);
glMatrixMode(GL_MODELVIEW);
but when the point's center is not on the screen (after panning with glOrthof), the whole point is not drawn. How can I have the point still render even when the center is not on the screen?
I don't believe there is anything you can do for an easy fix. Primitives are clipped before rasterization, so if that point lies outside the view frustum, it's not going to be rasterized, even if the rasterization would create fragments that do lie inside the view frustum.
Either switch to real quads with GL_TRIANGLES/GL_QUADS, or if you really don't want to do that, you can render your points to an offscreen buffer with size slightly larger than the viewport, and then blit the center of that image back onto the main frame.
I have a textured object in my OpenGL ES scene (version 1.1) for which I want to change the alpha to 0.5.
I am trying the following code :
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_NORMAL_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glEnable(GL_BLEND);
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
glColor4f(1.0, 1.0, 1.0, 0.5);
glVertexPointer(3, GL_FLOAT, 0, vertexes);
glNormalPointer(GL_FLOAT, 0, normals);
glTexCoordPointer(2, GL_FLOAT, 0, textures);
GLfloat ambientAndDiffuse[] = kAmbience;
glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT_AND_DIFFUSE, ambientAndDiffuse);
GLfloat specular[] = kSpecular;
glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, specular);
glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, kShininess);
GLfloat emission[] = kEmission;
glMaterialfv(GL_FRONT_AND_BACK, GL_EMISSION, emission);
glDrawElements(GL_TRIANGLES, vertexCount, GL_UNSIGNED_SHORT, indices);
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_NORMAL_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glDisable(GL_BLEND);
The problem is that the transparency of the model is not changing. The model is displayed on the screen correctly, however the alpha is still 1.
EDIT
My textures are jpgs. Do I need to save these as PNGs ?
Can anyone spot how I can correct this ?
Thank you.
Ah think I've solved it - you need to turn off the lighting and then it seems to work.
glDisable(GL_LIGHTING);
Have you set the texture environment variable to modulate? Like this:
glTexEnvi (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
That tells OpenGL to multiply the object's color by the texture's color. Also, I don't remember if you need to use a GL_COLOR_ARRY with glDrawElements() instead of just setting the current color.
I've been trying to figure out how to make a powder toy style game on the iPhone. My problem is how to draw pixels to the screen. From what I've read, OpenGL is better for games as it is faster/hardware accelerated, but there is no method to draw pixels directly to the screen. Apparently drawing pixels to an off-screen frame buffer is the way to go, but how do I then pass this to OpenGL? Do I use a texture?
(this is assuming I have no previous knowledge of iPhone graphics programming).
Thanks!
Usually in OpenGL you draw primitives and polygons. If you need to draw a bitmap, then you need to apply texture for your polygon.
Check out cocos2d-iphone engine for 2D games based on OpenGL.
If you still need to draw a pixel, here is a method from cocos2d to draw a line:
void ccDrawLine( CGPoint origin, CGPoint destination )
{
CGPoint vertices[2];
vertices[0] = origin;
vertices[1] = destination;
// Default GL states: GL_TEXTURE_2D, GL_VERTEX_ARRAY, GL_COLOR_ARRAY, GL_TEXTURE_COORD_ARRAY
// Needed states: GL_VERTEX_ARRAY,
// Unneeded states: GL_TEXTURE_2D, GL_TEXTURE_COORD_ARRAY, GL_COLOR_ARRAY
glDisable(GL_TEXTURE_2D);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glDisableClientState(GL_COLOR_ARRAY);
glVertexPointer(2, GL_FLOAT, 0, vertices);
glDrawArrays(GL_LINES, 0, 2);
// restore default state
glEnableClientState(GL_COLOR_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glEnable(GL_TEXTURE_2D);
}
I have a texture with transparency (the white triangle with that lighting information), and just can't make it's alpha variable.
alt text http://gotoandplay.freeblog.hu/files/alpha_help.png
The drawing code, with the missing piece:
//Place polygon vertices to the bottom left within the view.
glLoadIdentity();
glTranslatef(centerX, centerY, 0);
//Draw "diffuse" layer.
glBindTexture(GL_TEXTURE_2D, spriteTexture[0]); //Bind.
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
//Offset during development only.
glLoadIdentity();
glTranslatef(centerX-10, centerY+10, 0);
//Draw "specular" layer.
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, spriteTexture[1]); //Bind.
//Some smart alpha scaling code needs here...
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
Could somebody please help me out with the appropriate lines of code?
Some glBlendFunc, or maybe glTextEnvi stuff I suppose.
Ok, I got it even if I don't understand what I did exactly.
//Place polygon vertices to the bottom left within the view.
glLoadIdentity();
glTranslatef(centerX, centerY, 0);
//--1
//Draw "diffuse" layer.
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, spriteTexture[0]); //Bind.
//Blending.
glBlendFunc(GL_ONE, GL_ONE);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
//--2
//Draw "specular" layer.
glBindTexture(GL_TEXTURE_2D, spriteTexture[1]); //Bind.
//Blending.
glColor4f(opacity, opacity, opacity, opacity);
glBlendFunc(GL_SRC_COLOR, GL_ONE_MINUS_SRC_ALPHA);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
I tried another way before...
glColor4f(1.0f, 1.0f, 1.0f, opacity);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
...but the second map was somehow "weaker".
I'm working with the iPhone OpenGLES implementation and I wish to endlessly scroll a texture across a simple surface (two triangles making up a rectangle). This should be straightforward, but it's not something I've done before and I must be missing something. I can rotate the texture fine, but translate does not work at all. Do I have a minor implementation issue or am I doing something fundamentally wrong?
// move texture
glMatrixMode(GL_TEXTURE);
glPushMatrix();
glLoadIdentity();
// increment offset - no reset for demo purposes
wallOffset += 1.0;
// move the texture - this does not work
glTranslatef(wallOffset,wallOffset,0.0);
// rotate the texture - this does work
//glRotatef(wallOffset, 1.0, 0.0, 0.0);
glMatrixMode(GL_MODELVIEW);
glBindTexture(GL_TEXTURE_2D, WallTexture.name);
glTexCoordPointer(2, GL_FLOAT, 0, coordinates);
// simple drawing code
glNormalPointer(GL_FLOAT, 0, normals);
glVertexPointer(3, GL_FLOAT, 0, vertices);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
// push matrix back
glMatrixMode(GL_TEXTURE);
glPopMatrix();
glMatrixMode(GL_MODELVIEW);
You're incrementing your texture offset by 1.0f; but textures coordinates are considered in the range [0, 1], so you're not actually changing the texture coordinates (assuming you've enabled some sort of wrapping).
Try changing that increment (try .01f, or maybe something depending on the framerate) and see if it works. If not, then it may have something to do with the texture parameters you've got enabled.