GLKit texture jagged - ios

Question

I'm trying implement GLKit texture painting, and it's looks too jagged
Creating texture from .png, got this code from Apple's GLPaing example
private func texture(fromName name: String) -> textureInfo_t {
var texId: GLuint = 0
var texture: textureInfo_t = (0, 0, 0)
let brushImage = UIImage(named: name)!.cgImage!
let width: size_t = brushImage.width
let height: size_t = brushImage.height
var brushData = [GLubyte](repeating: 0, count: width * height * 4)
let bitmapInfo = CGImageAlphaInfo.premultipliedLast.rawValue
let brushContext = CGContext(data: &brushData, width: width, height: height, bitsPerComponent: 8, bytesPerRow: width * 4, space: (brushImage.colorSpace!), bitmapInfo: bitmapInfo)
brushContext?.draw(brushImage, in: CGRect(x: 0.0, y: 0.0, width: width.g, height: height.g))
glGenTextures(1, &texId)
// Bind the texture name.
glBindTexture(GL_TEXTURE_2D.ui, texId)
// Set the texture parameters to use a minifying filter and a linear filer (weighted average)
glTexParameteri(GL_TEXTURE_2D.ui, GL_TEXTURE_MIN_FILTER.ui, GL_LINEAR)
// Specify a 2D texture image, providing the a pointer to the image data in memory
glTexImage2D(GL_TEXTURE_2D.ui, 0, GL_RGBA, width.i, height.i, 0, GL_RGBA.ui, GL_UNSIGNED_BYTE.ui, brushData)
// Release the image data; it's no longer needed
texture.id = texId
texture.width = width.i
texture.height = height.i
return texture
}
and rendering while painting
private func renderLine(from _start: CGPoint, to _end: CGPoint) {
struct Static {
static var vertexBuffer: [GLfloat] = []
}
var count = 0
EAGLContext.setCurrent(context)
glBindFramebuffer(GL_FRAMEBUFFER.ui, viewFramebuffer)
// Convert locations from Points to Pixels
let scale = self.contentScaleFactor
var start = _start
start.x *= scale
start.y *= scale
var end = _end
end.x *= scale
end.y *= scale
// Allocate vertex array buffer
// Add points to the buffer so there are drawing points every X pixels
count = max(Int(ceilf(sqrtf((end.x - start.x).f * (end.x - start.x).f + (end.y - start.y).f * (end.y - start.y).f) / kBrushPixelStep.f)), 1)
Static.vertexBuffer.reserveCapacity(count * 2)
Static.vertexBuffer.removeAll(keepingCapacity: true)
for i in 0..<count {
Static.vertexBuffer.append(start.x.f + (end.x - start.x).f * (i.f / count.f))
Static.vertexBuffer.append(start.y.f + (end.y - start.y).f * (i.f / count.f))
}
// Load data to the Vertex Buffer Object
glBindBuffer(GL_ARRAY_BUFFER.ui, vboId)
glBufferData(GL_ARRAY_BUFFER.ui, count*2*MemoryLayout<GLfloat>.size, Static.vertexBuffer, GL_DYNAMIC_DRAW.ui)
glEnableVertexAttribArray(ATTRIB_VERTEX.ui)
glVertexAttribPointer(ATTRIB_VERTEX.ui, 2, GL_FLOAT.ui, GL_FALSE.ub, 0, nil)
// Draw
glUseProgram(program[PROGRAM_POINT].id)
glDrawArrays(GL_POINTS.ui, 0, count.i)
// Display the buffer
glBindRenderbuffer(GL_RENDERBUFFER.ui, viewRenderbuffer)
context.presentRenderbuffer(GL_RENDERBUFFER.l)
}
How could I improve texture quality?
UPDATE:
Even with bigger resolution .png result same. What is wrong am I doing?
There 1024x1024 .png with transparent background that I'm using: