SDL2 + OPENGLES 2.0 Output a blank GUI

[haorenhl007]

I use SDL2(v2.0.8) lib and OPENGLES 2.0 to test IMGUI，but I get an error output like follow(only a background without anything)：

The project files are follow：
https://github.com/haorenhl007/imguitest

Please tell me what wrong with my codes.
Thanks to everyone!

[ocornut]

Hello,

It's difficult to tell what's wrong exactly.

First, please start from the latest imgui version. Your version is very old and there's no reason to be using this old code if you are starting on a new project.

We could provide a imgui_impl_gles.cpp renderer in replacement of imgui_impl_opengl3.cpp

---

GLES3
According to @avaskoog the changes needed for GLES3 are:

• Change the #version XXX string the shader You pass a different string for it when calling ImGui_ImplOpenGL3_Init(). They used "#version 300 es\nprecision mediump float;" for GLES3. I am not sure what GLES2 needs.

• They also changed

GLint last_blend_src; glGetIntegerv(GL_BLEND_SRC, &last_blend_src);
GLint last_blend_dst; glGetIntegerv(GL_BLEND_DST, &last_blend_dst);

to

GLint last_blend_src_rgb; glGetIntegerv(GL_BLEND_SRC_RGB, &last_blend_src_rgb);
GLint last_blend_dst_rgb; glGetIntegerv(GL_BLEND_DST_RGB, &last_blend_dst_rgb);
GLint last_blend_src_alpha; glGetIntegerv(GL_BLEND_SRC_ALPHA, &last_blend_src_alpha);
GLint last_blend_dst_alpha; glGetIntegerv(GL_BLEND_DST_ALPHA, &last_blend_dst_alpha);

• at the bottom of the render function

glBlendFuncSeparate(last_blend_src_rgb, last_blend_dst_rgb, last_blend_src_alpha, last_blend_dst_alpha)

It is difficult for me because I don't have access to GLES2 devices but I am sure many people have done that renderer loop change before.

---

GLES2

This PR #336 based on an old version has GLES2 code
https://github.com/ocornut/imgui/pull/336/files
Most of the code is identical to the code used in the version the PR is based.

Maybe only the shaders needs to be changed to:

    const GLchar *vertex_shader =
        "uniform mat4 ProjMtx;\n"
        "attribute vec2 Position;\n"
        "attribute vec2 UV;\n"
        "attribute vec4 Color;\n"
        "varying vec2 Frag_UV;\n"
        "varying vec4 Frag_Color;\n"
        "void main()\n"
        "{\n"
        "	Frag_UV = UV;\n"
        "	Frag_Color = Color;\n"
        "	gl_Position = ProjMtx * vec4(Position.xy,0,1);\n"
        "}\n";

    const GLchar* fragment_shader =
        // WebGL requires precision specifiers but OpenGL 2.1 disallows
        // them, so I define the shader without it and then add it here.
        "precision mediump float;\n"

        "uniform sampler2D Texture;\n"
        "varying vec2 Frag_UV;\n"
        "varying vec4 Frag_Color;\n"
        "void main()\n"
        "{\n"
        "	gl_FragColor = Frag_Color * texture2D(Texture, Frag_UV);\n"
        "}\n";

Could you try with those shaders?

[haorenhl007]

Hello,
@ocornut , thanks for your reply.
I use qt, gles 2.0 to test imgui(the old version), it's normal, the code as follow:
https://github.com/haorenhl007/qtimgui-test
The shaders you provide are same to mine.
I try to correct the problem with the latest imgui version, code as follow:
https://github.com/haorenhl007/imguitest5
it still output a black screen.

[ocornut]

A step toward the solution would be to start testing for GL errors.
Maybe start testing for function returns and GL Errors, with the initialization stuff, for example test the return value of glCompileShader, call glGetShaderInfoLog, etc. Unfortunately the sample code doesn't validate all function calls properly.
edit I think maybe shader #version string is required?
If your platform has an OpenGL debugger it would make things easier.

One possibility is to debug the ES 2 renderer on PC using https://github.com/google/angle

I also don't know if SDL is conflicting somehow. I'll call in some people for advices.

[haorenhl007]

Hello,
@ocornut , thanks for your reply.
I have not much experience to test gles2.
I just use a simple example with sdl2 and gles2.0，it acts normal。
You can refer that。

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>

#ifdef __EMSCRIPTEN__
#include <emscripten/emscripten.h>
#endif

#include "SDL_test_common.h"

#if defined(__IPHONEOS__) || defined(__ANDROID__) || defined(__EMSCRIPTEN__) || defined(__NACL__) \
    || defined(__WINDOWS__) || defined(__LINUX__)
#define HAVE_OPENGLES2
#endif

#ifdef HAVE_OPENGLES2

#include "SDL_opengles2.h"

typedef struct GLES2_Context
{
#define SDL_PROC(ret,func,params) ret (APIENTRY *func) params;
#include "../src/render/opengles2/SDL_gles2funcs.h"
#undef SDL_PROC
} GLES2_Context;


static SDLTest_CommonState *state;
static SDL_GLContext *context = NULL;
static int depth = 16;
static GLES2_Context ctx;

static int LoadContext(GLES2_Context * data)
{
#if SDL_VIDEO_DRIVER_UIKIT
#define __SDL_NOGETPROCADDR__
#elif SDL_VIDEO_DRIVER_ANDROID
#define __SDL_NOGETPROCADDR__
#elif SDL_VIDEO_DRIVER_PANDORA
#define __SDL_NOGETPROCADDR__
#endif

#if defined __SDL_NOGETPROCADDR__
#define SDL_PROC(ret,func,params) data->func=func;
#else
#define SDL_PROC(ret,func,params) \
    do { \
        data->func = SDL_GL_GetProcAddress(#func); \
        if ( ! data->func ) { \
            return SDL_SetError("Couldn't load GLES2 function %s: %s", #func, SDL_GetError()); \
        } \
    } while ( 0 );
#endif /* __SDL_NOGETPROCADDR__ */

#include "../src/render/opengles2/SDL_gles2funcs.h"
#undef SDL_PROC
    return 0;
}

/* Call this instead of exit(), so we can clean up SDL: atexit() is evil. */
static void
quit(int rc)
{
    int i;

    if (context != NULL) {
        for (i = 0; i < state->num_windows; i++) {
            if (context[i]) {
                SDL_GL_DeleteContext(context[i]);
            }
        }

        SDL_free(context);
    }

    SDLTest_CommonQuit(state);
    exit(rc);
}

#define GL_CHECK(x) \
        x; \
        { \
          GLenum glError = ctx.glGetError(); \
          if(glError != GL_NO_ERROR) { \
            SDL_Log("glGetError() = %i (0x%.8x) at line %i\n", glError, glError, __LINE__); \
            quit(1); \
          } \
        }

/* 
 * Simulates desktop's glRotatef. The matrix is returned in column-major 
 * order. 
 */
static void
rotate_matrix(float angle, float x, float y, float z, float *r)
{
    float radians, c, s, c1, u[3], length;
    int i, j;

    radians = (float)(angle * M_PI) / 180.0f;

    c = SDL_cosf(radians);
    s = SDL_sinf(radians);

    c1 = 1.0f - SDL_cosf(radians);

    length = (float)SDL_sqrt(x * x + y * y + z * z);

    u[0] = x / length;
    u[1] = y / length;
    u[2] = z / length;

    for (i = 0; i < 16; i++) {
        r[i] = 0.0;
    }

    r[15] = 1.0;

    for (i = 0; i < 3; i++) {
        r[i * 4 + (i + 1) % 3] = u[(i + 2) % 3] * s;
        r[i * 4 + (i + 2) % 3] = -u[(i + 1) % 3] * s;
    }

    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++) {
            r[i * 4 + j] += c1 * u[i] * u[j] + (i == j ? c : 0.0f);
        }
    }
}

/* 
 * Simulates gluPerspectiveMatrix 
 */
static void 
perspective_matrix(float fovy, float aspect, float znear, float zfar, float *r)
{
    int i;
    float f;

    f = 1.0f/SDL_tanf(fovy * 0.5f);

    for (i = 0; i < 16; i++) {
        r[i] = 0.0;
    }

    r[0] = f / aspect;
    r[5] = f;
    r[10] = (znear + zfar) / (znear - zfar);
    r[11] = -1.0f;
    r[14] = (2.0f * znear * zfar) / (znear - zfar);
    r[15] = 0.0f;
}

/* 
 * Multiplies lhs by rhs and writes out to r. All matrices are 4x4 and column
 * major. In-place multiplication is supported.
 */
static void
multiply_matrix(float *lhs, float *rhs, float *r)
{
    int i, j, k;
    float tmp[16];

    for (i = 0; i < 4; i++) {
        for (j = 0; j < 4; j++) {
            tmp[j * 4 + i] = 0.0;

            for (k = 0; k < 4; k++) {
                tmp[j * 4 + i] += lhs[k * 4 + i] * rhs[j * 4 + k];
            }
        }
    }

    for (i = 0; i < 16; i++) {
        r[i] = tmp[i];
    }
}

/* 
 * Create shader, load in source, compile, dump debug as necessary.
 *
 * shader: Pointer to return created shader ID.
 * source: Passed-in shader source code.
 * shader_type: Passed to GL, e.g. GL_VERTEX_SHADER.
 */
void 
process_shader(GLuint *shader, const char * source, GLint shader_type)
{
    GLint status = GL_FALSE;
    const char *shaders[1] = { NULL };
    char buffer[1024];
    GLsizei length;

    /* Create shader and load into GL. */
    *shader = GL_CHECK(ctx.glCreateShader(shader_type));

    shaders[0] = source;

    GL_CHECK(ctx.glShaderSource(*shader, 1, shaders, NULL));

    /* Clean up shader source. */
    shaders[0] = NULL;

    /* Try compiling the shader. */
    GL_CHECK(ctx.glCompileShader(*shader));
    GL_CHECK(ctx.glGetShaderiv(*shader, GL_COMPILE_STATUS, &status));

    /* Dump debug info (source and log) if compilation failed. */
    if(status != GL_TRUE) {
        ctx.glGetProgramInfoLog(*shader, sizeof(buffer), &length, &buffer[0]);
        buffer[length] = '\0';
        SDL_Log("Shader compilation failed: %s", buffer);fflush(stderr);
        quit(-1);
    }
}

/* 3D data. Vertex range -0.5..0.5 in all axes.
* Z -0.5 is near, 0.5 is far. */
const float _vertices[] =
{
    /* Front face. */
    /* Bottom left */
    -0.5,  0.5, -0.5,
    0.5, -0.5, -0.5,
    -0.5, -0.5, -0.5,
    /* Top right */
    -0.5,  0.5, -0.5,
    0.5,  0.5, -0.5,
    0.5, -0.5, -0.5,
    /* Left face */
    /* Bottom left */
    -0.5,  0.5,  0.5,
    -0.5, -0.5, -0.5,
    -0.5, -0.5,  0.5,
    /* Top right */
    -0.5,  0.5,  0.5,
    -0.5,  0.5, -0.5,
    -0.5, -0.5, -0.5,
    /* Top face */
    /* Bottom left */
    -0.5,  0.5,  0.5,
    0.5,  0.5, -0.5,
    -0.5,  0.5, -0.5,
    /* Top right */
    -0.5,  0.5,  0.5,
    0.5,  0.5,  0.5,
    0.5,  0.5, -0.5,
    /* Right face */
    /* Bottom left */
    0.5,  0.5, -0.5,
    0.5, -0.5,  0.5,
    0.5, -0.5, -0.5,
    /* Top right */
    0.5,  0.5, -0.5,
    0.5,  0.5,  0.5,
    0.5, -0.5,  0.5,
    /* Back face */
    /* Bottom left */
    0.5,  0.5,  0.5,
    -0.5, -0.5,  0.5,
    0.5, -0.5,  0.5,
    /* Top right */
    0.5,  0.5,  0.5,
    -0.5,  0.5,  0.5,
    -0.5, -0.5,  0.5,
    /* Bottom face */
    /* Bottom left */
    -0.5, -0.5, -0.5,
    0.5, -0.5,  0.5,
    -0.5, -0.5,  0.5,
    /* Top right */
    -0.5, -0.5, -0.5,
    0.5, -0.5, -0.5,
    0.5, -0.5,  0.5,
};

const float _colors[] =
{
    /* Front face */
    /* Bottom left */
    1.0, 0.0, 0.0, /* red */
    0.0, 0.0, 1.0, /* blue */
    0.0, 1.0, 0.0, /* green */
    /* Top right */
    1.0, 0.0, 0.0, /* red */
    1.0, 1.0, 0.0, /* yellow */
    0.0, 0.0, 1.0, /* blue */
    /* Left face */
    /* Bottom left */
    1.0, 1.0, 1.0, /* white */
    0.0, 1.0, 0.0, /* green */
    0.0, 1.0, 1.0, /* cyan */
    /* Top right */
    1.0, 1.0, 1.0, /* white */
    1.0, 0.0, 0.0, /* red */
    0.0, 1.0, 0.0, /* green */
    /* Top face */
    /* Bottom left */
    1.0, 1.0, 1.0, /* white */
    1.0, 1.0, 0.0, /* yellow */
    1.0, 0.0, 0.0, /* red */
    /* Top right */
    1.0, 1.0, 1.0, /* white */
    0.0, 0.0, 0.0, /* black */
    1.0, 1.0, 0.0, /* yellow */
    /* Right face */
    /* Bottom left */
    1.0, 1.0, 0.0, /* yellow */
    1.0, 0.0, 1.0, /* magenta */
    0.0, 0.0, 1.0, /* blue */
    /* Top right */
    1.0, 1.0, 0.0, /* yellow */
    0.0, 0.0, 0.0, /* black */
    1.0, 0.0, 1.0, /* magenta */
    /* Back face */
    /* Bottom left */
    0.0, 0.0, 0.0, /* black */
    0.0, 1.0, 1.0, /* cyan */
    1.0, 0.0, 1.0, /* magenta */
    /* Top right */
    0.0, 0.0, 0.0, /* black */
    1.0, 1.0, 1.0, /* white */
    0.0, 1.0, 1.0, /* cyan */
    /* Bottom face */
    /* Bottom left */
    0.0, 1.0, 0.0, /* green */
    1.0, 0.0, 1.0, /* magenta */
    0.0, 1.0, 1.0, /* cyan */
    /* Top right */
    0.0, 1.0, 0.0, /* green */
    0.0, 0.0, 1.0, /* blue */
    1.0, 0.0, 1.0, /* magenta */
};

const char* _shader_vert_src = 
" attribute vec4 av4position; "
" attribute vec3 av3color; "
" uniform mat4 mvp; "
" varying vec3 vv3color; "
" void main() { "
"    vv3color = av3color; "
"    gl_Position = mvp * av4position; "
" } ";

const char* _shader_frag_src = 
" precision lowp float; "
" varying vec3 vv3color; "
" void main() { "
"    gl_FragColor = vec4(vv3color, 1.0); "
" } ";

typedef struct shader_data
{
    GLuint shader_program, shader_frag, shader_vert;

    GLint attr_position;
    GLint attr_color, attr_mvp;

    int angle_x, angle_y, angle_z;

} shader_data;

static void
Render(unsigned int width, unsigned int height, shader_data* data)
{
    float matrix_rotate[16], matrix_modelview[16], matrix_perspective[16], matrix_mvp[16];

    /* 
    * Do some rotation with Euler angles. It is not a fixed axis as
    * quaterions would be, but the effect is cool. 
    */
    rotate_matrix((float)data->angle_x, 1.0f, 0.0f, 0.0f, matrix_modelview);
    rotate_matrix((float)data->angle_y, 0.0f, 1.0f, 0.0f, matrix_rotate);

    multiply_matrix(matrix_rotate, matrix_modelview, matrix_modelview);

    rotate_matrix((float)data->angle_z, 0.0f, 1.0f, 0.0f, matrix_rotate);

    multiply_matrix(matrix_rotate, matrix_modelview, matrix_modelview);

    /* Pull the camera back from the cube */
    matrix_modelview[14] -= 2.5;

    perspective_matrix(45.0f, (float)width/height, 0.01f, 100.0f, matrix_perspective);
    multiply_matrix(matrix_perspective, matrix_modelview, matrix_mvp);

    GL_CHECK(ctx.glUniformMatrix4fv(data->attr_mvp, 1, GL_FALSE, matrix_mvp));

    data->angle_x += 3;
    data->angle_y += 2;
    data->angle_z += 1;

    if(data->angle_x >= 360) data->angle_x -= 360;
    if(data->angle_x < 0) data->angle_x += 360;
    if(data->angle_y >= 360) data->angle_y -= 360;
    if(data->angle_y < 0) data->angle_y += 360;
    if(data->angle_z >= 360) data->angle_z -= 360;
    if(data->angle_z < 0) data->angle_z += 360;

    GL_CHECK(ctx.glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT));
    GL_CHECK(ctx.glDrawArrays(GL_TRIANGLES, 0, 36));
}

int done;
Uint32 frames;
shader_data *datas;

void loop()
{
    SDL_Event event;
    int i;
    int status;

    /* Check for events */
    ++frames;
    while (SDL_PollEvent(&event) && !done) {
        switch (event.type) {
        case SDL_WINDOWEVENT:
            switch (event.window.event) {
                case SDL_WINDOWEVENT_RESIZED:
                    for (i = 0; i < state->num_windows; ++i) {
                        if (event.window.windowID == SDL_GetWindowID(state->windows[i])) {
                            int w, h;
                            status = SDL_GL_MakeCurrent(state->windows[i], context[i]);
                            if (status) {
                                SDL_Log("SDL_GL_MakeCurrent(): %s\n", SDL_GetError());
                                break;
                            }
                            /* Change view port to the new window dimensions */
                            SDL_GL_GetDrawableSize(state->windows[i], &w, &h);
                            ctx.glViewport(0, 0, w, h);
                            state->window_w = event.window.data1;
                            state->window_h = event.window.data2;
                            /* Update window content */
                            Render(event.window.data1, event.window.data2, &datas[i]);
                            SDL_GL_SwapWindow(state->windows[i]);
                            break;
                        }
                    }
                    break;
            }
        }
        SDLTest_CommonEvent(state, &event, &done);
    }
    if (!done) {
      for (i = 0; i < state->num_windows; ++i) {
          status = SDL_GL_MakeCurrent(state->windows[i], context[i]);
          if (status) {
              SDL_Log("SDL_GL_MakeCurrent(): %s\n", SDL_GetError());

              /* Continue for next window */
              continue;
          }
          Render(state->window_w, state->window_h, &datas[i]);
          SDL_GL_SwapWindow(state->windows[i]);
      }
    }
#ifdef __EMSCRIPTEN__
    else {
        emscripten_cancel_main_loop();
    }
#endif
}

int
main(int argc, char *argv[])
{
    int fsaa, accel;
    int value;
    int i;
    SDL_DisplayMode mode;
    Uint32 then, now;
    int status;
    shader_data *data;

    /* Initialize parameters */
    fsaa = 0;
    accel = 0;

    /* Initialize test framework */
    state = SDLTest_CommonCreateState(argv, SDL_INIT_VIDEO);
    if (!state) {
        return 1;
    }
    for (i = 1; i < argc;) {
        int consumed;

        consumed = SDLTest_CommonArg(state, i);
        if (consumed == 0) {
            if (SDL_strcasecmp(argv[i], "--fsaa") == 0) {
                ++fsaa;
                consumed = 1;
            } else if (SDL_strcasecmp(argv[i], "--accel") == 0) {
                ++accel;
                consumed = 1;
            } else if (SDL_strcasecmp(argv[i], "--zdepth") == 0) {
                i++;
                if (!argv[i]) {
                    consumed = -1;
                } else {
                    depth = SDL_atoi(argv[i]);
                    consumed = 1;
                }
            } else {
                consumed = -1;
            }
        }
        if (consumed < 0) {
            SDL_Log ("Usage: %s %s [--fsaa] [--accel] [--zdepth %%d]\n", argv[0],
                    SDLTest_CommonUsage(state));
            quit(1);
        }
        i += consumed;
    }

    /* Set OpenGL parameters */
    state->window_flags |= SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_BORDERLESS;
    state->gl_red_size = 5;
    state->gl_green_size = 5;
    state->gl_blue_size = 5;
    state->gl_depth_size = depth;
    state->gl_major_version = 2;
    state->gl_minor_version = 0;
    state->gl_profile_mask = SDL_GL_CONTEXT_PROFILE_ES;

    if (fsaa) {
        state->gl_multisamplebuffers=1;
        state->gl_multisamplesamples=fsaa;
    }
    if (accel) {
        state->gl_accelerated=1;
    }
    if (!SDLTest_CommonInit(state)) {
        quit(2);
        return 0;
    }

    context = (SDL_GLContext *)SDL_calloc(state->num_windows, sizeof(context));
    if (context == NULL) {
        SDL_Log("Out of memory!\n");
        quit(2);
    }
    
    /* Create OpenGL ES contexts */
    for (i = 0; i < state->num_windows; i++) {
        context[i] = SDL_GL_CreateContext(state->windows[i]);
        if (!context[i]) {
            SDL_Log("SDL_GL_CreateContext(): %s\n", SDL_GetError());
            quit(2);
        }
    }

    /* Important: call this *after* creating the context */
    if (LoadContext(&ctx) < 0) {
        SDL_Log("Could not load GLES2 functions\n");
        quit(2);
        return 0;
    }



    if (state->render_flags & SDL_RENDERER_PRESENTVSYNC) {
        SDL_GL_SetSwapInterval(1);
    } else {
        SDL_GL_SetSwapInterval(0);
    }

    SDL_GetCurrentDisplayMode(0, &mode);
    SDL_Log("Screen bpp: %d\n", SDL_BITSPERPIXEL(mode.format));
    SDL_Log("\n");
    SDL_Log("Vendor     : %s\n", ctx.glGetString(GL_VENDOR));
    SDL_Log("Renderer   : %s\n", ctx.glGetString(GL_RENDERER));
    SDL_Log("Version    : %s\n", ctx.glGetString(GL_VERSION));
    SDL_Log("Extensions : %s\n", ctx.glGetString(GL_EXTENSIONS));
    SDL_Log("\n");

    status = SDL_GL_GetAttribute(SDL_GL_RED_SIZE, &value);
    if (!status) {
        SDL_Log("SDL_GL_RED_SIZE: requested %d, got %d\n", 5, value);
    } else {
        SDL_Log( "Failed to get SDL_GL_RED_SIZE: %s\n",
                SDL_GetError());
    }
    status = SDL_GL_GetAttribute(SDL_GL_GREEN_SIZE, &value);
    if (!status) {
        SDL_Log("SDL_GL_GREEN_SIZE: requested %d, got %d\n", 5, value);
    } else {
        SDL_Log( "Failed to get SDL_GL_GREEN_SIZE: %s\n",
                SDL_GetError());
    }
    status = SDL_GL_GetAttribute(SDL_GL_BLUE_SIZE, &value);
    if (!status) {
        SDL_Log("SDL_GL_BLUE_SIZE: requested %d, got %d\n", 5, value);
    } else {
        SDL_Log( "Failed to get SDL_GL_BLUE_SIZE: %s\n",
                SDL_GetError());
    }
    status = SDL_GL_GetAttribute(SDL_GL_DEPTH_SIZE, &value);
    if (!status) {
        SDL_Log("SDL_GL_DEPTH_SIZE: requested %d, got %d\n", depth, value);
    } else {
        SDL_Log( "Failed to get SDL_GL_DEPTH_SIZE: %s\n",
                SDL_GetError());
    }
    if (fsaa) {
        status = SDL_GL_GetAttribute(SDL_GL_MULTISAMPLEBUFFERS, &value);
        if (!status) {
            SDL_Log("SDL_GL_MULTISAMPLEBUFFERS: requested 1, got %d\n", value);
        } else {
            SDL_Log( "Failed to get SDL_GL_MULTISAMPLEBUFFERS: %s\n",
                    SDL_GetError());
        }
        status = SDL_GL_GetAttribute(SDL_GL_MULTISAMPLESAMPLES, &value);
        if (!status) {
            SDL_Log("SDL_GL_MULTISAMPLESAMPLES: requested %d, got %d\n", fsaa,
                   value);
        } else {
            SDL_Log( "Failed to get SDL_GL_MULTISAMPLESAMPLES: %s\n",
                    SDL_GetError());
        }
    }
    if (accel) {
        status = SDL_GL_GetAttribute(SDL_GL_ACCELERATED_VISUAL, &value);
        if (!status) {
            SDL_Log("SDL_GL_ACCELERATED_VISUAL: requested 1, got %d\n", value);
        } else {
            SDL_Log( "Failed to get SDL_GL_ACCELERATED_VISUAL: %s\n",
                    SDL_GetError());
        }
    }

    datas = (shader_data *)SDL_calloc(state->num_windows, sizeof(shader_data));

    /* Set rendering settings for each context */
    for (i = 0; i < state->num_windows; ++i) {

        int w, h;
        status = SDL_GL_MakeCurrent(state->windows[i], context[i]);
        if (status) {
            SDL_Log("SDL_GL_MakeCurrent(): %s\n", SDL_GetError());

            /* Continue for next window */
            continue;
        }
        SDL_GL_GetDrawableSize(state->windows[i], &w, &h);
        ctx.glViewport(0, 0, w, h);

        data = &datas[i];
        data->angle_x = 0; data->angle_y = 0; data->angle_z = 0;

        /* Shader Initialization */
        process_shader(&data->shader_vert, _shader_vert_src, GL_VERTEX_SHADER);
        process_shader(&data->shader_frag, _shader_frag_src, GL_FRAGMENT_SHADER);

        /* Create shader_program (ready to attach shaders) */
        data->shader_program = GL_CHECK(ctx.glCreateProgram());

        /* Attach shaders and link shader_program */
        GL_CHECK(ctx.glAttachShader(data->shader_program, data->shader_vert));
        GL_CHECK(ctx.glAttachShader(data->shader_program, data->shader_frag));
        GL_CHECK(ctx.glLinkProgram(data->shader_program));

        /* Get attribute locations of non-fixed attributes like color and texture coordinates. */
        data->attr_position = GL_CHECK(ctx.glGetAttribLocation(data->shader_program, "av4position"));
        data->attr_color = GL_CHECK(ctx.glGetAttribLocation(data->shader_program, "av3color"));

        /* Get uniform locations */
        data->attr_mvp = GL_CHECK(ctx.glGetUniformLocation(data->shader_program, "mvp"));

        GL_CHECK(ctx.glUseProgram(data->shader_program));

        /* Enable attributes for position, color and texture coordinates etc. */
        GL_CHECK(ctx.glEnableVertexAttribArray(data->attr_position));
        GL_CHECK(ctx.glEnableVertexAttribArray(data->attr_color));

        /* Populate attributes for position, color and texture coordinates etc. */
        GL_CHECK(ctx.glVertexAttribPointer(data->attr_position, 3, GL_FLOAT, GL_FALSE, 0, _vertices));
        GL_CHECK(ctx.glVertexAttribPointer(data->attr_color, 3, GL_FLOAT, GL_FALSE, 0, _colors));

        GL_CHECK(ctx.glEnable(GL_CULL_FACE));
        GL_CHECK(ctx.glEnable(GL_DEPTH_TEST));
    }

    /* Main render loop */
    frames = 0;
    then = SDL_GetTicks();
    done = 0;

#ifdef __EMSCRIPTEN__
    emscripten_set_main_loop(loop, 0, 1);
#else
    while (!done) {
        loop();
    }
#endif

    /* Print out some timing information */
    now = SDL_GetTicks();
    if (now > then) {
        SDL_Log("%2.2f frames per second\n",
               ((double) frames * 1000) / (now - then));
    }
#if !defined(__ANDROID__) && !defined(__NACL__)  
    quit(0);
#endif    
    return 0;
}

#else /* HAVE_OPENGLES2 */

int
main(int argc, char *argv[])
{
    SDL_Log("No OpenGL ES support on this system\n");
    return 1;
}

#endif /* HAVE_OPENGLES2 */

/* vi: set ts=4 sw=4 expandtab: */

I will try to use angle to test ES2.

[haorenhl007]

Hello,
@ocornut,
I installed a opengl es 2.0 emulator on Ubuntu(PC)，imguitest5 act normal as follow：

I tested on ARM linux with a wayland background， it showed a black window wihout any errors。
I also tested on ARM linux without any GUI background，it showed no GUI, but showed errors as follow：
# ./imguitest5-noqt
vdk_create_display(880): wl_display_connect failed
SDL window error
I have two questiones:

1. Does SDL2 or the example need any libs else?
2. Is the test example need any or certain GUI platform interfaces?

[ocornut]

Does SDL2 or the example need any libs else?
Is the test example need any or certain GUI platform interfaces?

I don't know what SDL2 needs. Each app in examples/ uses a different technology for creating a window and rendering. None of it depends on GUI platform interface, and core imgui.* files don't have any hard platform dependency.

I think your problem is just a shader problem. You should try the more recent imgui_impl_opengl3.cpp which has support for most OpenGL variants and it now checks the shader compilation correctness. Older versions of that file didn't check that the shader compiled correctly, now we do. We those checks in you can debug the situation.

Also check others ES discussions or pull requests:
opengl

[haorenhl007]

Hello,
@ocornut, I succeed in solving this problem of blank GUI.
I changed the code (https://github.com/haorenhl007/imguitest5) according to the SDL2 example of
"testgles2".
I think the problem is that SDL2 did not initialize the GUI interface very well.
So I use the code follows to accomplish it.
` /* Initialize test framework /
state = SDLTest_CommonCreateState(argv, SDL_INIT_VIDEO);
if (!state) {
return 1;
}
/ Set OpenGL parameters */
state->window_flags |= SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_BORDERLESS;
state->gl_red_size = 5;
state->gl_green_size = 5;
state->gl_blue_size = 5;
state->gl_depth_size = depth;
state->gl_major_version = 2;
state->gl_minor_version = 0;
state->gl_profile_mask = SDL_GL_CONTEXT_PROFILE_ES;

if (!SDLTest_CommonInit(state)) {
    quit(2);
    return 0;
}

`
the code is now runing on wayland, but not well on no GUI platform interfaces, I will follow this.
Now I test my new code, it acts not very good:

1. the framerate is about 32, I want it to be about 60.
2. If I move the mouse cursor inside the GUI, It become black until the curosr is moved out.

would you please give me some advice or website link about imgui showing picture or 3d objects？
I appreciate your help!

[ktb92677]

Any updates on this? My OpenGLES2 instance is also running at around 32fps and I want it to be running at around 60