带有OpenGL ES 2.0的SDL2-无法在iOS上绘制简单的三角形

Question

I am using SDL2 to test out OpenGL ES 2.0 and for some reason I am unable to draw anything on the screen. I properly configured my shaders and it compiled correctly and binded by vertex attributes as well but still nothing. The triangle does draw if I compile the app for MacOSX or Windows.

Here's my shader:

[VERTEX SHADER]

attribute vec3 vPosition;

void main() {
    gl_Position = vec4(vPosition.xyz, 1.0);
}

[FRAGMENT SHADER]

precision mediump float;

varying vec4 _color;

void main() {
    gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
}

Also note that before linking the shader I call this:

glBindAttribLocation(programObj, 0, "vPosition");

[DRAWING CODE]

glUseProgram(programObj);

GLfloat vVertices[] = {0.0f, 0.5f, 0.0f,
            -0.5f, -0.5f, 0.0f,
            0.5f, -0.5f, 0.0f};

glViewport(0, 0, 320, 480);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

// Load the vertex data
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, vVertices);
glEnableVertexAttribArray(0);
glDrawArrays(GL_TRIANGLES, 0, 3);

SDL_GL_SwapWindow(window);

As I mentioned before, this works fine on MacOSX or Windows but when I compile it for iOS, nothing draws. Can anyone point out what I am doing wrong?

Answer 1

This probably means that your initialization code is not complete. To make sure everything is initialized you can create SDL renderer, which will initialize everything necessary. You do not have to use it for your drawing after creation.

SDL_Renderer *renderer = SDL_CreateRenderer(window, -1, 0);

If you find this solution too dirty and hackish, you can examine the source code of SDL_CreateRenderer and add missing parts to your code.

I had the same problem when I was porting an OpenGL game to iOS, creating the renderer fixed the issue.