iPhone OpenGL ES Paint App Brush Effect - iphone

Question

I'm developing painting app [taking reference from GLPaint app] for iPhone and iPad.
I am working on brush effect. I want to get brush effect for my paint app as shown in Image1
I've got brush stroke similar to image 2
I am using following code for brush texture:
CGImageRef brushImage;
CGContextRef brushContext;
GLubyte *brushData;
size_t width, height;
if(UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)
{
brushImage = [UIImage imageNamed:#"flower#2x.png"].CGImage;
}
else {
brushImage = [UIImage imageNamed:#"flower.png"].CGImage;
}
width = CGImageGetWidth(brushImage) ;
height = CGImageGetHeight(brushImage) ;
if(brushImage) {
brushData = (GLubyte *) calloc(width * height * 4, sizeof(GLubyte));
brushContext = CGBitmapContextCreate(brushData, width, height, 8, width * 4, CGImageGetColorSpace(brushImage),kCGImageAlphaPremultipliedLast);
CGContextDrawImage(brushContext, CGRectMake(0.0, 0.0, (CGFloat)width, (CGFloat)height), brushImage);
CGContextRelease(brushContext);
glGenTextures(1, &brushTexture);
glBindTexture(GL_TEXTURE_2D, brushTexture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, brushData);
free(brushData);
}
CGFloat scale;
scale = self.contentScaleFactor;
glMatrixMode(GL_PROJECTION);
CGRect frame = self.bounds;
glLoadIdentity();
glOrthof(0, (frame.size.width) * scale, 0, (frame.size.height) * scale, -1, 1);
glViewport(0, 0, (frame.size.width) * scale, (frame.size.height) * scale);
glMatrixMode(GL_MODELVIEW);
glDisable(GL_DITHER);
glEnable(GL_BLEND);
glEnable(GL_TEXTURE_2D);
glEnableClientState(GL_VERTEX_ARRAY);
glEnable(GL_BLEND);
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
glEnable(GL_POINT_SPRITE_OES);
glTexEnvf(GL_POINT_SPRITE_OES, GL_COORD_REPLACE_OES, GL_TRUE);
glPointSize(width / kBrushScale);
// Define a starting color
HSL2RGB((CGFloat) 0.0 / (CGFloat)kPaletteSize, kSaturation, kLuminosity, &components[0], &components[1], &components[2]);
glColor4f(components[0] * kBrushOpacity, components[1] * kBrushOpacity, components[2] * kBrushOpacity, kBrushOpacity);
I've been searching for code related to different paint brush stroke but I cannot find any code. Help me to get "desired" brush stroke similar to image1.

Answer 1

Do not use GL_POINT_SPRITE_OES mode. Draw sprites via standard triangles. Then it needs to bind sprite texture coords to the target output coords and make sprite texture repeatable.
Assuming sprite texture size is 32x32. The default texture coords is in rect {{0,0},{1.0,1.0}}. For drawing sprite at {x,y} position, it needs to use sprite texture coord based on rect {{(x%32)/32.0, (y%32)/32.0},{1.0, 1.0}}. This way it prevents sprite content from smudging.