Jeff Molofee - NeHe's OpenGL Tutorials

Also notice that I add xspeed to the x axis moving speed, and yspeed to the y axis moving speed. This gives us control over what direction the particles move later in the program.

particle[loop].xi = xspeed+float((rand()%60)-32.0f); // X Axis Speed And Direction

particle[loop].yi = yspeed+float((rand()%60)-30.0f); // Y Axis Speed And Direction

particle[loop].zi = float((rand()%60)-30.0f); // Z Axis Speed And Direction

Lastly we assign the particle a new color. The variable col holds a number from 0 to 11 (12 colors). We use this variable to look of the red, green and blue intensities in our color table that we made at the beginning of the program. The first line below sets the red (r) intensity to the red value stored in colors[col][0]. So if col was 0, the red intensity would be 1.0f. The green and blue values are read the same way.

If you don't understand how I got the value of 1.0f for the red intensity if col is 0, I'll explain in a bit more detail. Look at the very top of the program. Find the line: static GLfloat colors[12][3]. Notice there are 12 groups of 3 number. The first of the three number is the red intensity. The second value is the green intensity and the third value is the blue intensity. [0], [1] and [2] below represent the 1st, 2nd and 3rd values I just mentioned. If col is equal to 0, we want to look at the first group. 11 is the last group (12th color).

particle[loop].r=colors[col][0]; // Select Red From Color Table

particle[loop].g=colors[col][1]; // Select Green From Color Table

particle[loop].b=colors[col][2]; // Select Blue From Color Table

}

The line below controls how much gravity there is pulling upward. By pressing 8 on the number pad, we increase the yg (y gravity) variable. This causes a pull upwards. This code is located here in the program because it makes our life easier by applying the gravity to all of our particles thanks to the loop. If this code was outside the loop we'd have to create another loop to do the same job, so we might as well do it here.

// If Number Pad 8 And Y Gravity Is Less Than 1.5 Increase Pull Upwards

if (keys[VK_NUMPAD8] && (particle[loop].yg<1.5f)) particle[loop].yg+=0.01f;

This line has the exact opposite affect. By pressing 2 on the number pad we decrease yg creating a stronger pull downwards.

// If Number Pad 2 And Y Gravity Is Greater Than –1.5 Increase Pull Downwards

if (keys[VK_NUMPAD2] && (particle[loop].yg>-1.5f)) particle[loop].yg-=0.01f;

Now we modify the pull to the right. If the 6 key on the number pad is pressed, we increase the pull to the right.

// If Number Pad 6 And X Gravity Is Less Than 1.5 Increase Pull Right

if (keys[VK_NUMPAD6] && (particle[loop].xg<1.5f)) particle[loop].xg+=0.01f;

Finally, if the 4 key on the number pad is pressed, our particle will pull more to the left. These keys give us some really cool results. For example, you can make a stream of particles shooting straight up in the air. By adding some gravity pulling downwards you can turn the stream of particles into a fountain of water!

// If Number Pad 4 And X Gravity Is Greater Than –1.5 Increase Pull Left

if (keys[VK_NUMPAD4] && (particle[loop].xg>-1.5f)) particle[loop].xg-=0.01f;

I added this bit of code just for fun. My brother thought the explosion was a cool effect :) By pressing the tab key all the particles will be reset back to the center of the screen. The moving speed of the particles will once again be multiplied by 10, creating a big explosion of particles. After the particles fade out, your original effect will again reappear.

if (keys[VK_TAB]) // Tab Key Causes A Burst

{

particle[loop].x=0.0f; // Center On X Axis

particle[loop].y=0.0f; // Center On Y Axis

particle[loop].z=0.0f; // Center On Z Axis

particle[loop].xi=float((rand()%50)-26.0f)*10.0f; // Random Speed On X Axis

particle[loop].yi=float((rand()%50)-25.0f)*10.0f; // Random Speed On Y Axis

particle[loop].zi=float((rand()%50)-25.0f)*10.0f; // Random Speed On Z Axis

}

}

}

return TRUE; // Everything Went OK

}

The code in KillGLWindow(), CreateGLWindow() and WndProc() hasn't changed, so we'll skip down to WinMain(). I'll rewrite the entire section of code to make it easier to follow through the code.

int WINAPI WinMain(HINSTANCE hInstance, // Instance

HINSTANCE hPrevInstance, // Previous Instance

LPSTR lpCmdLine, // Command Line Parameters

int nCmdShow) // Window Show State

{

MSG msg; // Windows Message Structure

BOOL done=FALSE; // Bool Variable To Exit Loop

// Ask The User Which Screen Mode They Prefer

if (MessageBox(NULL, "Would You Like To Run In Fullscreen Mode?", "Start FullScreen?", MB_YESNO|MB_ICONQUESTION) == IDNO) {

fullscreen=FALSE; // Windowed Mode

}

// Create Our OpenGL Window

if (!CreateGLWindow("NeHe's Particle Tutorial", 640, 480, 16, fullscreen)) {

return 0; // Quit If Window Was Not Created

}

This is our first change to WinMain(). I've added some code to check if the user decide to run in fullscreen mode or windowed mode. If they decide to use fullscreen mode, I change the variable slowdown to 1.0f instead of 2.0f. You can leave this bit code out if you want. I added the code to speed up fullscreen mode on my 3dfx (runs ALOT slower than windowed mode for some reason).

if (fullscreen) // Are We In Fullscreen Mode ( ADD )

{

slowdown=1.0f; // Speed Up The Particles (3dfx Issue) ( ADD )

}

while(!done) // Loop That Runs Until done=TRUE

{

if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) // Is There A Message Waiting?

{

if (msg.message==WM_QUIT) // Have We Received A Quit Message?

{

done=TRUE; // If So done=TRUE

} else // If Not, Deal With Window Messages

{

TranslateMessage(&msg); // Translate The Message

DispatchMessage(&msg); // Dispatch The Message

}

} else // If There Are No Messages

{

if ((active && !DrawGLScene()) || keys[VK_ESCAPE]) // Updating View Only If Active

{

done=TRUE; // ESC or DrawGLScene Signalled A Quit

} else // Not Time To Quit, Update Screen

{

SwapBuffers(hDC); // Swap Buffers (Double Buffering)

I was a little sloppy with the next bit of code. Usually I don't include everything on one line, but it makes the code look a little cleaner :)

The line below checks to see if the + key on the number pad is being pressed. If it is and slowdown is greater than 1.0f we decrease slowdown by 0.01f. This causes the particles to move faster. Remember in the code above when I talked about slowdown and how it affects the speed at which the particles travel.

if (keys[VK_ADD] && (slowdown>1.0f)) slowdown-=0.01f; // Speed Up Particles

This line checks to see if the – key on the number pad is being pressed. If it is and slowdown is less than 4.0f we increase the value of slowdown. This causes our particles to move slower. I put a limit of 4.0f because I wouldn't want them to move much slower. You can change the minimum and maximum speeds to whatever you want :)