J.Doe J.Doe - 1 month ago 8x
Swift Question

Having issues with drawing to a frame buffer texture. It draws blank

I am in OpenGL es 2.0 with glKit trying to render to iOS devices.

Basically my goal is to instead of drawing to the main buffer draw to a texture. Then render that texture to the screen. I have been trying to follow another topic on so. Unfortunately they mention something about the power of two (im assuming with regards to resolution) but I don't know how to fix it. Anyway here is my swift interpretation of the code from that topic.

import Foundation
import GLKit
import OpenGLES

class RenderTexture {
var framebuffer:GLuint = 0
var tex:GLuint = 0
var old_fbo:GLint = 0

init(width: GLsizei, height: GLsizei)
glGetIntegerv(GLenum(GL_FRAMEBUFFER_BINDING), &old_fbo)

glGenFramebuffers(1, &framebuffer)
glGenTextures(1, &tex)

glBindFramebuffer(GLenum(GL_FRAMEBUFFER), framebuffer)
glBindTexture(GLenum(GL_TEXTURE_2D), tex)
glTexImage2D(GLenum(GL_TEXTURE_2D), 0, GL_RGBA, GLsizei(width), GLsizei(height), 0, GLenum(GL_RGBA), GLenum(GL_UNSIGNED_BYTE), nil)
glFramebufferTexture2D(GLenum(GL_FRAMEBUFFER), GLenum(GL_COLOR_ATTACHMENT0), GLenum(GL_TEXTURE_2D), tex, 0)

glClearColor(0, 0.1, 0, 1)

let status = glCheckFramebufferStatus(GLenum(GL_FRAMEBUFFER))
if (status != GLenum(GL_FRAMEBUFFER_COMPLETE))
print("DIDNT GO WELL WITH", width, " " , height)

glBindFramebuffer(GLenum(GL_FRAMEBUFFER), GLenum(old_fbo))

func begin()
glGetIntegerv(GLenum(GL_FRAMEBUFFER_BINDING), &old_fbo)
glBindFramebuffer(GLenum(GL_FRAMEBUFFER), framebuffer)

func end()
glBindFramebuffer(GLenum(GL_FRAMEBUFFER), GLenum(old_fbo))

Then as far as rendering I have some things going on.

A code that theoretically renders any texture full screen. This has been tested with two manually loaded pngs (using no buffer changes) and works great.

func drawTriangle(texture: GLuint)
//glViewport(0, 0, width, height)
//glClearColor(0, 0.0, 0, 1.0)
//glClear(GLbitfield(GL_COLOR_BUFFER_BIT) | GLbitfield(GL_DEPTH_BUFFER_BIT))


let loc1 = glGetUniformLocation(texShader, "s_texture")
glUniform1i(loc1, 0)

let loc3 = glGetUniformLocation(texShader, "matrix")
if (loc3 != -1)
glUniformMatrix4fv(loc3, 1, GLboolean(GL_FALSE), &matrix)

glBindTexture(GLenum(GL_TEXTURE_2D), texture)
glDrawArrays(GLenum(GL_TRIANGLE_STRIP), 0, 6)


I also have a function that draws a couple dots on the screen. You dont really need to see the methods but it works. This is how I am going to know that OpenGL is drawing from the buffer texture and NOT a preloaded texture.

Finally here is the gist of the code I am trying to do.

func initialize()
nfbo = RenderTexture(width: width, height: height)

fun draw()
glViewport(0, 0, GLsizei(width * 2), GLsizei(height * 2)) //why do I have to multiply for 2 to get it to work?????
drawDots() //Draws the dots

At the end of all this all that is drawn is a blank screen. If there is any more code that would help you figure things out let me know. I tried to trim it to make it less annoying for you.

Note: Considering the whole power of two thing I have tried passing the fbo class 512 x 512 just in case it would make things work being a power of two. Unfortunately it didnt do that.

Another Note: All I am doing is going to be 2D so I dont need depth buffers right?


yesterday I saw exactly the same issue.

after struggling for hours, I found out why.

the trick is configuring your texture map with the following:

    glTexParameteri(GLenum(GL_TEXTURE_2D), GLenum(GL_TEXTURE_WRAP_S), GL_CLAMP_TO_EDGE);
    glTexParameteri(GLenum(GL_TEXTURE_2D), GLenum(GL_TEXTURE_WRAP_T), GL_CLAMP_TO_EDGE);

otherwise, you won't draw anything on the texture map.

the reason seems to be that while ios supports texture maps that are not power of 2. it requires GL_CLAMP_TO_EDGE. otherwise it won't work.

it should really report incomplete framebuffer. it took me quite long time to debug this problem!

here a related discussion:

Rendering to non-power-of-two texture on iPhone