How to draw a dotted line using OpenGL ES 1? - opengl-es

Question

To draw a dotted line in OpenGL I can use glLineStipple, but how do I achieve the same effect in OpenGL ES 1?

Answer 1

Lines can be textured, just like triangles. Enable alpha testing, apply an alpha texture, set up some texture coordinates, and enjoy.

Answer 2

Actually i have realized the doted line or the dashed line using for loops but it still make non sense to use it as a line type link to the drawing method, here is the code of my doted line and dashed line below:
doted line:
(void)drawVerticalDotedInternalGrid{
float a,b;
int drawCount =0;
GLfloat dotedInternalGrid[1296];
for (a = -0.5f; a <= 0.5f; a +=0.5f) {
for (b = -0.875f; b <=0.925f; b += 0.025f)
{
dotedInternalGrid[drawCount] = b;
drawCount++;
dotedInternalGrid[drawCount] = a;
drawCount++;
};
};
glPointSize(1.0f);
glColor4f(0.863f,0.863f,0.863f,0.8f); //line color
glVertexPointer(2, GL_FLOAT, 0, dotedInternalGrid);
glEnableClientState(GL_VERTEX_ARRAY);
glDrawArrays(GL_POINTS, 0, 648);
glDisableClientState(GL_VERTEX_ARRAY);
}
dashed line:
(void)drawVerticalDashedInternalGridH{
GLfloat dashedLine[1296];
float a,b;
int i =0;
//-0.4----0.4 // -0.875----0.900
for (a = -0.4f; a <= 0.4f; a +=0.1f) {
for (b =-0.825f; b <=0.950f; b+=0.025f) {
dashedLine[i] = b;
i++;
dashedLine[i] = a;
i++;
};
};
//glLineWidth(1.0f);
glColor4f(0.863f,0.863f,0.863f,1.f); //line color
glVertexPointer(2, GL_FLOAT, 0, dashedLine);
glEnableClientState(GL_VERTEX_ARRAY);
glDrawArrays(GL_LINES, 0, 648);
glDisableClientState(GL_VERTEX_ARRAY);
}
of course ye can see the code is drawing in a rectangle area of certain coordinates,the bother things is how to figure out the dotedInternalGrid[1296]; this size of array dynamically for draw method use and the number of lines to draw as well.

Answer 3

To explain it easily, I have put drawHorizontalDashedLine() first.
To understand, click this image.
I cannot put an image on this post because of my reputation.
Visualizing the Vertices
+(void)drawHorizontalDashedLine:(GLfloat)x1 x2:(GLfloat)x2 y:(GLfloat)y {
//Parameters
GLfloat DASH_LENGTH = 4.0f;
GLfloat GAP_LENGTH = 2.0f;
GLfloat LINE_THICKNESS = 1.5f;
//Calculate how many dashes require to draw the whole line
GLfloat fHorizontalLength = fabsf(x2-x1);
int nDashedLineCount = fHorizontalLength / (DASH_LENGTH + GAP_LENGTH);
int nVerticesSize = nDashedLineCount * 4; //A dashed line has 4 values(2 points)
//Vertex
GLfloat vertices[nVerticesSize];
//The first dashed line vertices
vertices[0] = (x1 < x2)? x1 : x2;
vertices[1] = y;
vertices[2] = (x1 < x2)? x1 : x2 + DASH_LENGTH;
vertices[3] = y;
//The other vertices of dashed lines
for (int nIndex=4; nIndex < nVerticesSize; nIndex=nIndex+4) {
vertices[nIndex] = vertices[nIndex-2] + GAP_LENGTH;
vertices[nIndex+1] = y;
vertices[nIndex+2] = vertices[nIndex] + DASH_LENGTH;
vertices[nIndex+3] = y;
//NSLog(#"Point1(%.2f, %.2f)", vertices[nIndex], vertices[nIndex+1]);
//NSLog(#"Point2(%.2f, %.2f)", vertices[nIndex+2], vertices[nIndex+3]);
}
//Draw the arrays
glPushMatrix();
glLineWidth(LINE_THICKNESS);
glVertexPointer (2, GL_FLOAT, 0, vertices);
glDrawArrays (GL_LINES, 0, nVerticesSize/2);
glPopMatrix();
}
drawDashedLine().
I used the trigonometric function to get lengths.
+(void)drawDashedLine:(CGPoint)point1 point2:(CGPoint)point2 {
//Parameters
GLfloat DASH_LENGTH = 3.0f;
GLfloat GAP_LENGTH = 1.0f;
GLfloat LINE_THICKNESS = 1.5f;
//Calculate how many dashes require to draw the whole line
GLfloat fWidth = point2.x - point1.x;
GLfloat fHeight = point2.y - point1.y;
GLfloat fRadian = atan2(fHeight, fWidth);
float fLineLength = sqrtf(powf(fWidth, 2) + powf(fHeight, 2));
int nDashedLineCount = fabsf(fLineLength / (DASH_LENGTH + GAP_LENGTH));
int nVerticesSize = nDashedLineCount * 4; //A dashed line has 4 values(2 points)
//Vertex
GLfloat vertices[nVerticesSize];
//The first dashed line vertices
vertices[0] = point1.x;
vertices[1] = point1.y;
vertices[2] = point1.x + cosf(fRadian) * DASH_LENGTH;
vertices[3] = point1.y + sinf(fRadian) * DASH_LENGTH;
//The other vertices of dashed lines
for (int nIndex=4; nIndex < nVerticesSize; nIndex=nIndex+4) {
vertices[nIndex] = vertices[nIndex-2] + cosf(fRadian) * GAP_LENGTH;
vertices[nIndex+1] = vertices[nIndex-1] + sinf(fRadian) * GAP_LENGTH;
vertices[nIndex+2] = vertices[nIndex] + cosf(fRadian) * DASH_LENGTH;
vertices[nIndex+3] = vertices[nIndex+1] + sinf(fRadian) * DASH_LENGTH;
//NSLog(#"DrawDash Point1(%.2f, %.2f)", vertices[nIndex], vertices[nIndex+1]);
//NSLog(#"DrawDash Point2(%.2f, %.2f)", vertices[nIndex+2], vertices[nIndex+3]);
}
//Draw the arrays
glPushMatrix();
glLineWidth(LINE_THICKNESS);
glVertexPointer (2, GL_FLOAT, 0, vertices);
glDrawArrays (GL_LINES, 0, nVerticesSize/2);
glPopMatrix();
}

Answer 4

glPushAttrib(GL_ENABLE_BIT);
# glPushAttrib is done to return everything to normal after drawing
glLineStipple(1, 0xAAAA); # [1]
glEnable(GL_LINE_STIPPLE);
glBegin(GL_LINES);
glVertex3f(-.5,.5,-.5);
glVertex3f(.5,.5,-.5);
glEnd();
glPopAttrib();