drawing multiple rectangles with Cairo graphics - c

I'm trying to write a Cairo program to black-fill the entire image and then draw another rectangle inside of it a different color. Eventually, I'm going to make this a program that generates a .png of the current time that looks like a digital clock. For now, this is where I'm getting hung up.
Here's my code:
#include <stdio.h>
#include <cairo.h>
//on color: 0.6, 1.0, 0
//off color: 0.2, 0.4, 0
int prop_number_width;
int prop_number_height;
int prop_width;
int prop_height;
int prop_space_width;
int prop_space_height;
double width;
double height;
double w_unit;
double h_unit;
void draw_number(cairo_t* cr, int unit_width, int num);
int main(int argc, char** argv) {
/* proportional sizes:
* the widths and heights of the diagram
*/
prop_number_width = 5; //how many spaces the number takes up
prop_number_height = 6;
prop_space_width = 1; //extra width on each side
prop_space_height = 1; //extra height on each side
prop_width = 25 + (2 * prop_space_width); //width of diagram
prop_height = 6 + (2 * prop_space_height); //height of diagram
/* actual sizes:
* the pixel value of different sizes
*/
width = 200.0;
height = 100.0;
w_unit = width / prop_width;
h_unit = height / prop_height;
//begin cairo stuff
cairo_surface_t* surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, (int)width, (int)height);
cairo_t* cr = cairo_create(surface);
//black fill
cairo_set_source_rgb(cr, 0.0, 0.0, 0.0);
cairo_rectangle(cr, 0.0, 0.0, width, height); //cr ref, x, y, width, height
cairo_fill_preserve(cr);
//draw numbers from left to right
draw_number(cr, 0, 1);
//draw_number(cr, 6, 3);
//draw_number(cr, 14, 3);
//draw_number(cr, 20, 7);
//draw in colons
cairo_destroy(cr);
cairo_surface_write_to_png(surface, "test.png");
cairo_surface_destroy(surface);
return 0;
}
void draw_number(cairo_t* cr, int unit_width, int num) {
//determine the box size that the number will be drawn in
double box_x = w_unit * (prop_space_width + unit_width);
double box_y = h_unit * prop_space_height;
double box_width = w_unit * prop_number_width;
double box_height = h_unit * prop_number_height;
printf("{box_x: %lf box_y: %lf} {box_width: %lf box_height: %lf}\n", box_x, box_y, box_width, box_height);
cairo_set_source_rgb(cr, 0.2, 0.4, 0);
cairo_rectangle(cr, box_x, box_y, box_width, box_height);
cairo_fill_preserve(cr);
}
The problem is with this code it draws the rectangle to take up the whole image where from the printf's it should only take up a small part. Does anybody know how I can make this rectangle show up as the correct size?

I should have looked at the API more carefully. I needed to do cairo_fill() instead of cairo_fill_preserve(). Apparently, the first call to cairo_fill_preserve() was keeping the original rectangle and always filling that one.

Related

Why is 3D projection in OpenGL working, but leaving a trail behind?

I just did some math from Wikipedia for 3D projection because I noticed they were simple, library not needed. It does work but, the cube leaves a trail behind as it moves. Note that the cube doesn't actually move, I am actually changing the camera position which makes he cube look like it's moving.
There's no need to point out 100 bad practices that I am doing, I'm aware, this is just supposed to be be a quick test.
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <glad/glad.h>
#include <SDL2/SDL.h>
#include <SDL2/SDL_image.h>
#include <SDL2/SDL_opengl.h>
#include <math.h>
#include "utils.h"
#include "keys.h"
char p = 1;
typedef struct Vec3 {
float x;
float y;
float z;
} Vec3;
void Mat_iden(float *m, Uint32 s) {
Uint32 i = 0;
Uint32 unt = s + 1;
while (i < s) {
m[unt * i] = 1;
i++;
}
}
float one[3][3];
float two[3][3];
float three[3][3];
int main() {
SDL_Init(SDL_INIT_VIDEO);
IMG_Init(IMG_INIT_PNG);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 5);
SDL_Window *w = SDL_CreateWindow("Snapdoop", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 500, 500, SDL_WINDOW_OPENGL);
SDL_GLContext c = SDL_GL_CreateContext(w);
gladLoadGLLoader((GLADloadproc)SDL_GL_GetProcAddress);
Mat_iden(one[0], 3);
Mat_iden(two[0], 3);
Mat_iden(three[0], 3);
Shader s[2];
s[0] = Shade("/home/shambhav/eclipse-workspace/Snadoop/src/vs.glsl");
s[1] = Shade("/home/shambhav/eclipse-workspace/Snadoop/src/fs.glsl");
Shade_comp(&s[0], GL_VERTEX_SHADER);
Shade_comp(&s[1], GL_FRAGMENT_SHADER);
Program sp;
Prog_attach(&sp, s, 2);
printf("VS: %s\n", s[0].info);
printf("FS: %s\n", s[1].info);
printf("SP: %s\n", sp.info);
glDeleteShader(s[0].c);
glDeleteShader(s[1].c);
float v[48] = {
//Front
0.25, 0.25, 0.25, 1.0, 1.0, 0.0,
-0.25, 0.25, 0.25, 1.0, 0.0, 0.0,
-0.25, -0.25, 0.25, 0.0, 1.0, 1.0,
0.25, -0.25, 0.25, 0.0, 1.0, 0.0,
//Back
0.25, 0.25, -0.25, 0.0, 0.0, 1.0,
-0.25, 0.25, -0.25, 1.0, 0.0, 1.0,
-0.25, -0.25, -0.25, 1.0, 1.0, 1.0,
0.25, -0.25, -0.25, 0.0, 0.0, 0.0
};
unsigned int i[36] = {
//Front
0, 1, 2,
2, 3, 0,
//Right
0, 3, 7,
7, 4, 0,
//Left
1, 2, 6,
6, 5, 2,
//Back
4, 5, 6,
6, 7, 4,
//Up
0, 1, 5,
5, 4, 0,
//Down
3, 7, 2,
2, 6, 7
};
GLuint VAO, VBO, EBO;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
glGenBuffers(1, &EBO);
glBindVertexArray(VAO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(v), v, GL_STATIC_DRAW);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(i), i, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(float) * 6, (void *)0);
glEnableVertexAttribArray(0);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(float) * 6, (void *)(sizeof(float) * 3));
glEnableVertexAttribArray(1);
Vec3 cam = {1.0, 1.0, 1.0};
Vec3 theta = {0, 0, 0};
Key k = (const Key){ 0 };
printf("%d\n", k.alpha[9]);
SDL_Event e;
while (p) {
while (SDL_PollEvent(&e)) {
switch (e.type) {
case SDL_QUIT:
p = 0;
break;
case SDL_KEYDOWN:
*key(&k, e.key.keysym.sym) = 1;
break;
case SDL_KEYUP:
*key(&k, e.key.keysym.sym) = 0;
break;
}
}
if (*key(&k, SDLK_RIGHT)) {
cam.x += 0.01;
}
if (*key(&k, SDLK_LEFT)) {
cam.x -= 0.01;
}
if (*key(&k, SDLK_UP)) {
cam.y += 0.01;
}
if (*key(&k, SDLK_DOWN)) {
cam.y -= 0.01;
}
if (*key(&k, 'w')) {
theta.y += 0.01;
}
if (*key(&k, 's')) {
theta.y -= 0.01;
}
if (*key(&k, 'a')) {
theta.x -= 0.01;
}
if (*key(&k, 'd')) {
theta.x += 0.01;
}
if (*key(&k, 'z')) {
theta.z -= 0.01;
}
if (*key(&k, 'x')) {
theta.z += 0.01;
}
if (*key(&k, 'n')) {
cam.z += 0.01;
}
if (*key(&k, 'm')) {
cam.z -= 0.01;
}
one[1][1] = cos(theta.x);
one[1][2] = sin(theta.x);
one[2][1] = -sin(theta.x);
one[2][2] = cos(theta.x);
two[0][0] = cos(theta.y);
two[0][2] = -sin(theta.y);
two[2][0] = sin(theta.y);
two[2][2] = cos(theta.y);
three[0][0] = cos(theta.z);
three[0][1] = sin(theta.z);
three[1][0] = -sin(theta.z);
three[1][1] = cos(theta.z);
glUseProgram(sp.p);
glUniformMatrix3fv(2, 1, GL_FALSE, one[0]);
glUniformMatrix3fv(3, 1, GL_FALSE, two[0]);
glUniformMatrix3fv(4, 1, GL_FALSE, three[0]);
glUniform3f(5, cam.x, cam.y, cam.z);
glClear(GL_DEPTH_BUFFER_BIT);
glDrawElements(GL_TRIANGLES, 36, GL_UNSIGNED_INT, 0);
SDL_GL_SwapWindow(w);
}
glDeleteProgram(sp.p);
glDeleteVertexArrays(1, &VAO);
glDeleteBuffers(1, &VBO);
glDeleteBuffers(1, &EBO);
SDL_GL_DeleteContext(c);
SDL_DestroyWindow(w);
SDL_Quit();
return 0;
}
Vertex Shader(vs.glsl):
#version 450 core
layout (location = 0) in vec3 pos;
layout (location = 1) in vec3 tcol;
layout (location = 2) uniform mat3 x;
layout (location = 3) uniform mat3 y;
layout (location = 4) uniform mat3 z;
layout (location = 5) uniform vec3 c;
out vec3 col;
void main() {
vec3 d = x * y * z * (pos - c);
gl_Position.x = d.x / d.z;
gl_Position.y = d.y / d.z;
gl_Position.z = 0.0;
gl_Position.w = 1.0;
col = tcol;
}
Fragment Shader:
#version 450 core
out vec4 color;
in vec3 col;
void main() {
color = vec4(col, 1.0);
}
I think that keys.h and utils.h should not be here as they are not relevant to OpenGL. And this is a Minimum Reproducible Example as the only extra parts(keys.h and utils.h) are required for managing key data and loading shaders respectively.
Some keys in my code may be inverted, it's just bad code in all ways... Sorry for that.
This is an image I have taken after moving the cube(or the camera perspective to be accurate). One major thing to note is that it seems to be working perfectly other than the trail.
You need to clear the color buffer as well:
glClear(GL_DEPTH_BUFFER_BIT);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glClear clears the specified buffers. The buffers are specified with a bit mask. GL_COLOR_BUFFER_BIT indicates to clear the buffers currently enabled for color writing.
The short answer is that you need to change:
glClear(GL_DEPTH_BUFFER_BIT);
...to...
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
More details
Comments have asked for more elaboration, so I'll elaborate.
When you say glClear(GL_DEPTH_BUFFER_BIT) it clears out the pixel values in the Z-Buffer (depth buffer). When you say glClear(GL_COLOR_BUFFER_BIT) it clears out the RGBA channels of the pixels in the color buffer (sets them to the glClearColor). If you say glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT) it clears both the Z-Buffer and the color buffer at the same time. That's what you want to do. You want to start each frame with a fresh black background and draw your content for that frame over top of it.
Think of it like setting each pixel to black and setting the depth value to zero. Actually, it will set the color buffer to the color specified by glClearColor and will set the depth value to the value specified by glClearDepth.
In your comment you said that you thought it "clears the functionality". That's not what glClear does. If you wanted to enable or disable writing to the depth buffer completely, you could do so with with glDepthMask. This function lets you completely disable writes to the depth buffer, potentially while still writing color values to the color buffer. There is a similar function called glColorMask that lets you select which channels of the color buffer (red, green, blue, and/or alpha) you want to write to as well. In this way you could potentially do interesting things like rendering only green, or even doing a special effect where you do a render pass in which you render only depth values and not color values (perhaps in preparation for knocking out a special effect to be applied in a subsequent pass.) glClear, conversely, actually sets the values in the pixels of the color buffer or depth buffer.
In the code you posted, you're only doing glClear(GL_DEPTH_BUFFER_BIT), which is only clearing the depth buffer, but not the color buffer. This essentially leaves all the paint on the canvas from last frame you drew, so leftover images from previous frames remain visible on the screen. You should be clearing both buffers.
Because you only draw your colorful square each frame, you draw a new square over top of whatever was in the buffer from last time. If you're double-buffering (common in full-screen graphics modes, but not windowed graphics modes), you may find that you're drawing over top of a frame from two-frames-ago, which may produce a strobing/flashing marquee effect.
The argument to glClear is called a bitmask. It uses each bit of the mask like a checkbox to select whether a particular kind of buffer should be cleared. Specifying GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT will logically OR the bits together creating a number with both bits set -- which is like checking both checkboxes, saying, "yes, please clear the depth buffer, and yes also clear the color buffer".
There can be up to four different kinds of buffers, not just color and depth. The four mask fields are GL_COLOR_BUFFER_BIT, GL_DEPTH_BUFFER_BIT, GL_ACCUM_BUFFER_BIT, and GL_STENCIL_BUFFER_BIT. Each one of these is a bit-field value, a number with a single binary bit set, which can be logically OR'ed together like 4 individual checkboxes. In your application your render target may not have an accumulator buffer or a stencil buffer. Some render targets don't even make use of a depth buffer. It's totally up to how you created your render buffer originally. In your case it looks like you have a buffer with color and depth. So when it comes time to clear the buffer, in preparation for rendering the frame, you'll want to make sure you check both boxes, effectively asking for both the color and depth components of your buffers to be cleared. Do so by passing GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT as the argument to glClear.
The use of bit-fields here is so exemplary, that glClear is actually used on the Wikipedia page for Mask_(computing) - Uses of bitmasks to explain how bitmasks can be used!

Get mouse click coordinates in OpenGL during animation?

I want to make a game in which when somebody clicks on the moving ball, it bursts. I have added the codes for animation and the mouse click event, but when the animation is going on, the click function is not working. When I tried it without the animation, it worked properly. I want to know why is this happening.
#include<stdio.h>
#include<GL/glut.h>
#include<unistd.h>
#include<math.h>
int x, y;
float mx, my;
float i, j;
void mouse(int button, int state, int mousex, int mousey)
{
if(button==GLUT_LEFT_BUTTON && state==GLUT_DOWN)
{
mx = mousex;
my = mousey;
printf("%f %f\n",mx,my);
glutPostRedisplay();
}
}
void init()
{
glClearColor(0.0, 0.0, 0.0, 1.0);
glColor3f(0.0, 1.0, 0.0);
glPointSize(1.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0, 1560, 0, 840);
}
int randValue()
{
int i = rand();
int num = i%1000;
return num;
}
void blast(int x, int y)
{
glBegin(GL_POLYGON);
glColor3f(1.0f,0.0f,0.0f);
glVertex2i(x-100, y-100);
glVertex2i(x, y-100);
glVertex2i(x-22, y-20);
glVertex2i(x-100, y-30);
glVertex2i(x-30, y-40);
glVertex2i(x-150, y-80);
glVertex2i(x-20, y);
glVertex2i(x, y-40);
glVertex2i(x-66, y-125);
glVertex2i(x-34, y-32);
glVertex2i(x-32, y-55);
glVertex2i(x-32, y);
glVertex2i(x-60, y-57);
glVertex2i(x-75, y-69);
glVertex2i(x-100, y);
glEnd();
glFlush();
}
void display()
{
int j = 0, k = 0, l = 1;
while(1)
{
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(0.0, 1.0, 0.0);
glBegin(GL_POINTS);
for (i = 0;i < 6.29;i += 0.001)
{
x = 100 * cos(i);
y = 100 * sin(i);
glVertex2i(x / 2 + j, y / 2 + k);
if((x / 2 + j) >= 1560 || (y / 2 + k) >= 840)
{
glEnd();
glFlush();
glClear(GL_COLOR_BUFFER_BIT);
blast(x / 2 + j, y / 2 + k);
sleep(2);
j = randValue();
k = 0;
}
}
j = j + 3;
k = k + 5;
glEnd();
glFlush();
}
}
int main (int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(1360, 768);
glutInitWindowPosition(0, 0);
glutCreateWindow("{Project}");
init();
glutDisplayFunc(display);
glutMouseFunc(mouse);
glutMainLoop();
}
Your code has an infinite loop inside the display function, thus you never give the control back to GLUT. GLUT already has an infinite loop like that inside glutMainLoop.
Instead you shall render only ONE frame in display, post glutPostRedisplay and return:
void display()
{
glClear(GL_COLOR_BUFFER_BIT);
// ... draw the frame here ...
// for exmaple:
i += 0.001;
float x = 100 * cos(i);
float y = 100 * sin(i);
glColor3f(0.0, 1.0, 0.0);
glBegin(GL_POINTS);
glVertex2f(x, y);
glEnd();
glFlush();
glutPostRedisplay();
}
Then your mouse function will be called and you'll be able to update the state as necessary.
There are two problems here:
OpenGL has no support for an input device by itself, you normally use OpenGL to present information but you have something else attached to the window where you present the info that is what gives you mouse access. this involves to know which is the other environment you are using that offers you a pointing device into the screen area.
if you have the window mouse coordinates you need to map well on the window you present your OpenGL output, but you have to convert them back to some point in your scene, but probably your ball is not there. There's some ambiguity when passing from a plane image representing a 3D scene to a point in that scene in 3D, as you have all points in the Z axis sharing the same screen coordinates in 2D screen. so you have to trace back to the possible position of the ball from the point of view (the camera), based on the window coordinates of the mouse. This is a geometrical problem that involves the inverse transformation of a projection, that is always singular.
you can solve this without having to guess, as you know where your ball is, you can redo the transformation that made it to appear in the two dimensional window, and then compare coordinates based on those. OpenGL allows you to know the actual transformation it is doing to represent your scene, and you can use it to see where in the screen your ball is represented (you don't need to do this for every vertex of the ball, only for the center, for example) and then check if your shot has gone close enough to hit the ball. You should consider also if some other object upper in the Z axis is in the way, so you don't kill anybody behind a wall.

OpenGL rectangle animation

I'm trying to 'animate' a rectangle's height based on a random number input. So with each new random number, the rectangle is re-drawn.
How do I do this?
My code:
#include <time.h>
#include <GL/freeglut.h>
#include <GL/gl.h>
float height;
int i;
/* display function - code from:
http://fly.cc.fer.hr/~unreal/theredbook/chapter01.html
This is the actual usage of the OpenGL library.
The following code is the same for any platform */
void renderFunction()
{
srand(time(NULL));
height = rand() % 10;
glClearColor(0.0, 0.0, 0.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(0.0, 0.0, 1.0);
glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);
glBegin(GL_POLYGON);
glVertex2f(-0.5, -0.5); // bottom left corner
glVertex2f(-0.5, height); // top left corner
glVertex2f(-0.3, height); // top right corner
glVertex2f(-0.3, -0.5); // bottom right corner
glEnd();
glFlush();
}
/* Main method - main entry point of application
the freeglut library does the window creation work for us,
regardless of the platform. */
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE);
glutInitWindowSize(900,600);
glutInitWindowPosition(100,100);
glutCreateWindow("OpenGL - First window demo");
glutDisplayFunc(renderFunction);
glutIdleFunc(renderFunction);
glutReshapeFunc(renderFunction);
glutMainLoop();
return 0;
}
While the program doesn't crash is simply draws a single rectangle.
Given that your sizes are in the range 0.0 <= dimension <= 1.0 and the height you calculate is in the range 0 <= height <= 9, you need to scale the random number like this:
height = (float)rand() / RAND_MAX;
Also please move srand(time(NULL)); from renderFunction() to main() otherwise your rectangle sizes will be clamped during every second.
The rand()%10 returns an integer which is usually greater than or equal to 1. So the height is mostly 1 since the maximum height it can render on the screen is 1.

Problems when dealing with lighting and shadowing in opengl

I am trying to put lights, materials and shadows to my robot arm but unfortunately something weird happens (please compile or see the below picture), now I am still annoying by
1) Not showing correct lighting and reflection properties as well as material properties
2) No shadow painted, although I have done the shadow casting in function "void showobj(void)"
I appreciate if anyone can help, I have already working for it 2 days with no progress :(
The following is my code
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <time.h>
#include <math.h>
#include <GL/glut.h>
#include "gsrc.h"
#include <Windows.h>
const double PI = 3.14159265;
// angles to rotate the base, lower and upper arms of the robot arm
static GLfloat theta, phi, psi = 0.0;
//Starting time
double startT;
//Time Diff variable
double dif,startTime,endTime,deltaT;
//define n
double n = 3;
//Set the parameters of the light number one
GLfloat Xs = 35.0;
GLfloat Ys = 35.0;
GLfloat Zs = 35.0;
//Shadow color
GLfloat shadowcolor[] = {0.0,0.0,0.0};
//initialize the window and everything to prepare for display
void init_gl() {
//set display color to white
glClearColor(1,1,1,0);
//clear and enable z-buffer
glClear (GL_DEPTH_BUFFER_BIT);
glEnable (GL_DEPTH_TEST);
//clear display window
glClear(GL_COLOR_BUFFER_BIT);
}
//Draw the base of the robot arm
void draw_base(){
glPushMatrix();
//to create the quadric objects
GLUquadric *qobj,*qobjl,*qobju;
qobj = gluNewQuadric();
qobjl = gluNewQuadric();
qobju = gluNewQuadric();
//set the color of the cylinder
glColor3f(1.0,0.0,0.0);
//Re-position the cylinder (x-z plane is the base)
glRotatef(-90,1.0,0.0,0.0);
//Draw the cylinder
gluCylinder(qobj, 30.0, 30.0, 40.0, 40.0, 40.0);
//Draw the upper disk of the base
gluDisk(qobju,0,30,40,40);
glPushMatrix();
//Change the M(lowdisk<updisk)
glTranslatef(0,0,40);
glColor3f(0,0,0);
//Draw the lower disk of the base
gluDisk(qobjl,0,30,40,40);
glPopMatrix();
glPopMatrix();
}
/***********************Texture Work Starts************************************/
//Load the raw file for texture
/* Global Declarations */
#define IW 256 // Image Width
#define IH 256 // Image Height
//3D array to store image data
unsigned char InputImage [IW][IH][4];
// Read an input image from a .raw file with double
void ReadRawImage ( unsigned char Image[][IH][4] )
{
FILE *fp;
int i, j, k;
char* filename;
unsigned char temp;
filename = "floor.raw";
if ((fp = fopen (filename, "rb")) == NULL)
{
printf("Error (ReadImage) : Cannot read the file!!\n");
exit(1);
}
for ( i=0; i<IW; i++)
{
for ( j=0; j<IH; j++)
{
for (k = 0; k < 3; k++) // k = 0 is Red k = 1 is Green K = 2 is Blue
{
fscanf(fp, "%c", &temp);
Image[i][j][k] = (unsigned char) temp;
}
Image[i][j][3] = (unsigned char) 0; // alpha = 0.0
}
}
fclose(fp);
}
/****************************Texture Work Ends***************************************/
/****************************Light and Shadows***************************************/
void lightsrc(){
GLfloat light1PosType [] = {Xs, Ys, Zs, 1.0};
//GLfloat light2PosType [] = {0.0, 100.0, 0.0, 0.0};
glLightfv(GL_LIGHT1, GL_POSITION, light1PosType);
//glEnable(GL_LIGHT1);
//glLightfv(GL_LIGHT2, GL_POSITION, light2PosType);
//glEnable(GL_LIGHT2);
GLfloat whiteColor[] = {1.0, 1.0, 1.0, 1.0};
GLfloat blackColor[] = {0.0, 0.0, 0.0, 1.0};
glLightfv(GL_LIGHT1, GL_AMBIENT, blackColor);
glLightfv(GL_LIGHT1, GL_DIFFUSE, whiteColor);
glLightfv(GL_LIGHT1, GL_SPECULAR, whiteColor);
glEnable(GL_LIGHT1);
glEnable( GL_LIGHTING );
}
/****************************Light and Shadows work ends***************************************/
//Draw the 2x2x2 cube with center (0,1,0)
void cube(){
glPushMatrix();
glTranslatef(0,1,0);
glutSolidCube(2);
glPopMatrix();
}
//Draw the lower arm
void draw_lower_arm(){
glPushMatrix();
glScalef(15.0/2.0,70.0/2.0,15.0/2.0);//scale half is enough (some part is in the negative side)
cube();
glPopMatrix();
}
//Draw the upper arm
void draw_upper_arm(){
glPushMatrix();
glScalef(15.0/2.0,40.0/2.0,15.0/2.0);//scale half is enough (some part is in the negative side)
cube();
glPopMatrix();
}
void drawCoordinates(){
glBegin (GL_LINES);
glColor3f (1,0,0);
glVertex3f (0,0,0);
glVertex3f (600,0,0);
glColor3f (0,1,0);
glVertex3f (0,0,0);
glVertex3f (0,600,0);
glColor3f (0,0,1);
glVertex3f (0,0,0);
glVertex3f (0,0,600);
glEnd();
}
//To draw the whole robot arm
void drawRobot(){
//Robot Drawing Starts
//Rotate the base by theta degrees
glRotatef(theta,0.0,1.0,0.0);
//Draw the base
draw_base();
//M(B<La)
glTranslatef(0.0,40.0,0.0);
//Rotate the lower arm by phi degree
glRotatef(phi,0.0,0.0,1.0);
//change the color of the lower arm
glColor3f(0.0,0.0,1.0);
//Draw the lower arm
draw_lower_arm();
//M(La<Ua)
glTranslatef(0.0,70.0,0.0);
//Rotate the upper arm by psi degree
glRotatef(psi,0.0,0.0,1.0);
//change the color of the upper arm
glColor3f(0.0,1.0,0.0);
//Draw the upper arm
draw_upper_arm();
//Drawing Finish
glutSwapBuffers();
}
void showobj(void) {
//set the projection and perspective parameters/arguments
GLint viewport[4];
glGetIntegerv( GL_VIEWPORT, viewport );
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective( 45, double(viewport[2])/viewport[3], 0.1, 1000 );
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(-200, 300, 200, 0, 0, 0, 0,1,0 );
// get the rotation matrix from the rotation user-interface
glMultMatrixf(gsrc_getmo() );
//Clear the display and ready to show the robot arm
init_gl();
//put the light source
lightsrc();
//Draw coordinates
drawCoordinates();
//give material properties
GLfloat diffuseCoeff[] = {0.2, 0.4, 0.9, 1.0}; // kdR= 0.2, kdG= 0.4, kdB= 0.9
GLfloat specularCoeff[] = {1.0, 1.0, 1.0, 1.0}; //
glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT_AND_DIFFUSE, diffuseCoeff);
glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, specularCoeff);
glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, 100.0 ); // ns= 25
//Draw the ground floor
glColor3f(0.4,0.4,0.4);
glPushMatrix();
glRotatef(90,1,0,0);
glRectf(-500,-500,500,500);
glPopMatrix();
int i,j;
GLfloat M[4][4];
for (i=0; i<4; i++){
for (j=0; j<4; j++){
M[i][j] = 0;
}
M[0][0]=M[1][1]=M[2][2]=1;
M[2][3]=-1.0/Zs;
}
//Start drawing shadow
drawRobot(); // draw the objects
glPushMatrix( ); // save state
glMatrixMode(GL_MODELVIEW);
glTranslatef(Xs, Ys, Zs);// Mwc←s
glMultMatrixf(M[4]);// perspective project
glTranslatef(-Xs, -Ys, -Zs);// Ms←wc
glColor3fv (shadowcolor);
//Draw the robot arm
drawRobot();
glPopMatrix(); // restore state
//Shadow drawing ends
glFlush ();
}
//To animate the robot arm
void animate(void)
{
//get the end time
endTime = timeGetTime();
//float angle;
//calculate deltaT
deltaT = (endTime - startTime); //in msecs
//float test;
float deltaTSecs = deltaT/1000.0f; //in secs
//apply moving equation
psi = (90.0) * 0.50 * (1-cos((deltaTSecs/(n+1)) * PI));
glutPostRedisplay ();
}
void main (int argc, char** argv)
{
glutInit(&argc, argv);
//DOUBLE mode better for animation
// Set display mode.
glutInitDisplayMode( GLUT_DOUBLE | GLUT_RGB);
glutInitWindowPosition( 50, 100 ); // Set top-left display-window position.
glutInitWindowSize( 400, 300 ); // Set display-window width and height.
glutCreateWindow( "Robot arm : my first self-learning opengl program" ); // Create display window.
// Register mouse-click and mouse-move glut callback functions
// for the rotation user-interface.
//Allow user to drag the mouse and view the object
glutMouseFunc( gsrc_mousebutton );
glutMotionFunc( gsrc_mousemove );
//record the starting time
startTime = timeGetTime();
// Display everything in showobj function
glutDisplayFunc(showobj);
//Perform background processing tasks or continuous animation
glutIdleFunc(animate);
glutMainLoop();
}
your screen flashes because you are calling glutSwapBuffers() in drawRobot(). That makes your screen repaint two times, once when you draw the robot, and once more when you draw the shadow. Also, you are missing glPushMatrix() at the beginning of drawRobot() and glPopMatrix() at the end. You need to put it there, otherwise it will affect rendering afterwards (the shadow will move with the upper link of the arm).
Then, you specify the shadow matrix wrong. Let's try this:
int i,j;
GLfloat M[4][4];
for (i=0; i<4; i++){
for (j=0; j<4; j++){
M[i][j] = 0;
}
}
M[0][0]=M[1][1]=M[2][2]=1;
M[2][3]=-1.0/Zs;
drawRobot(); // draw the objects
//Start drawing shadow
glEnable(GL_CULL_FACE);
glDisable(GL_LIGHTING); // want constant-color shadow
glPushMatrix( ); // save state
glMatrixMode(GL_MODELVIEW);
glTranslatef(Xs, Ys, Zs);// Mwc←s
glMultMatrixf(&M[0][0]);// perspective project
glTranslatef(-Xs, -Ys, -Zs);// Ms←wc
glColor3fv (shadowcolor);
//Draw the robot arm
drawRobot();
glPopMatrix(); // restore state
glDisable(GL_CULL_FACE);
glEnable(GL_LIGHTING); // enable again ...
//Shadow drawing ends
Also, you can see i've added GL_CULL_FACE arround the shadow, it is to avoid depth fighting. This more or less fixes it technically.
But still - the shadow position is calculated incorrectly. Let's try looking at projection shadows.
So first, we need to have position for the ground plane and for the light:
float g[] = {0, 1, 0, 0}; // ground plane
float l[] = {20, 300, 50, 1}; // light position and "1"
That is a plane equation and a homogenous light position (normal 3D position, padded with a "1"). Then you throw away your shadow matrix setup (glTranslatef(), glMultMatrixf() and glTranslatef()) and call myShadowMatrix(g, l) instead, so it becomes:
glPushMatrix( ); // save state
glMatrixMode(GL_MODELVIEW);
float g[] = {0, 1, 0, 0}; // ground plane
float l[] = {20, 300, 50, 1}; // light position and "1"
myShadowMatrix(g, l);
glColor3fv (shadowcolor);
//Draw the robot arm
drawRobot();
glPopMatrix(); // restore state
And that mostly does work. There is still a lot of z-fighting going on, and the shadow has four different colors. As for the colors, stop calling glColor3f() in drawRobot(), as for the z-fighting, use this:
glPolygonOffset(-1, -1);
glEnable(GL_POLYGON_OFFSET_FILL);
// before
// draw shadow
glDisable(GL_POLYGON_OFFSET_FILL);
// afterwards
And that makes one nice planar shadows demo :). Cheers ...
sw.

Using the following function that draws a filled circle in opengl, how do I make it show at different coordinates of the window?

I have got the following code to draw a filled circle in opengl. The problem is that it draws at the center of the screen. How do I make it draw in another position of it?
Here is the code:
#define CIRCLE_RADIUS = 0.15f
int circle_points = 100;
void draw()
{
glClear(GL_COLOR_BUFFER_BIT);
double angle = 2* PI/circle_points ;
glPolygonMode( GL_FRONT, GL_FILL );
glColor3f(0.2, 0.5, 0.5 );
glBegin(GL_POLYGON);
double angle1 = 0.0;
glVertex2d( CIRCLE_RADIUS * cos(0.0) , CIRCLE_RADIUS * sin(0.0));
int i;
for (i = 0; i < circle_points; i++)
{
glVertex2d(CIRCLE_RADIUS * cos(angle1), CIRCLE_RADIUS *sin(angle1));
angle1 += angle ;
}
glEnd();
glFlush();
}
The obvious way would be to call glTranslate first. Note, however, that you can already accomplish the same a bit more easily with a combination of glPointSize and glPoint:
glPointSize(CIRCLE_RADIUS/2.0f);
glPoint(center_x, center_y, center_z);
Before you start drawing the circles, you'll want something like:
glEnable(GL_POINT_SMOOTH);
glHint(GL_POINT_SMOOTH_HINT, GL_NICEST);
Otherwise, your "circles" could end up as squares.
Edit: Without knowing how you've set up your coordinates, it's impossible to know what the "top-left" position is, but you could do something like this:
void draw_circle(float x, float y, float radius) {
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();
glTranslatef(x, y, 0.0f);
static const int circle_points = 100;
static const float angle = 2.0f * 3.1416f / circle_points;
// this code (mostly) copied from question:
glBegin(GL_POLYGON);
double angle1=0.0;
glVertex2d(radius * cos(0.0) , radius * sin(0.0));
int i;
for (i=0; i<circle_points; i++)
{
glVertex2d(radius * cos(angle1), radius *sin(angle1));
angle1 += angle;
}
glEnd();
glPopMatrix();
}
You could then call (for example):
draw_circle(0.0f, 0.0f, 0.2f); // centered
draw_circle(1.0f, 0.0f, 0.2f); // right of center
draw_circle(1.0f, 1.0f, 0.2f); // right and up from center
Of course, the directions I've given assume haven't (for example) rotated your view, so x increases to the right and y increases upward.

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